Abstract
Background
Future efficacy testing of candidate vaccines and other interventions to prevent HIV will require engagement of vulnerable populations. Here, we assessed willingness to participate in future clinical trials among participants recruited for an HIV incidence study in western Kenya.
Materials and methods
From February 2017 to May 2018, we recruited people living without HIV who reported multiple sexual partners into a 24-month HIV incidence cohort study in Kisumu County, Kenya. At screening for study eligibility and study exit, participants completed comprehensive sociobehavioral questionnaires. They were also provided a general definition of a clinical trial and asked if they would be willing to participate in a future clinical trial of a candidate HIV vaccine. At enrollment, participants were also asked about facilitators and barriers to participation in such a clinical trial.
Results
Among 940 individuals screened for enrollment into the HIV incidence study, 919 (97.8%) reported willingness to participate in a future clinical trial of a candidate HIV vaccine. Willing individuals were more likely than unwilling ones to have exchanged sex for goods or money (60.1% vs. 35.0%, p = 0.0237) and were less likely to believe that an individual’s HIV status can be inferred by looking at them (8.7% vs. 23.8%, p = 0.0175). Willingness to participate was similarly common among participants who enrolled (608/618, 98.4%) and completed the study (518/533, 97.2%). The vast majority of the 618 enrolled participants reported obtaining HIV research information from radio/TV (n = 608, 98.1%) and newspapers/magazines/brochures (n = 579, 93.1%). Advantages they identified included HIV education (n = 594, 95.8%), access to healthcare (n = 576, 93.2%), and HIV counseling/testing (n = 574, 92.9%). Among 271 female participants, 235 (86.7%) identified free pregnancy testing as an advantage while 28 (19.4%) were unlikely to participate in a study that required the use of contraception. Among 10 enrollees who were unwilling to participate, five (50%) cited a fear of acquiring HIV and five (50%) cited fear of vaccine adverse effects.
Conclusions
We identified a highly willing population for future testing of HIV preventive vaccines. Specific barriers to participation should be addressed in recruitment efforts.
Supplementary Information
The online version contains supplementary material available at 10.1186/s12889-026-27840-0.
Keywords: AIDS Vaccines; HIV Infections; Kenya; Health Knowledge, Attitudes, Practice; Surveys and Questionnaires
Background
HIV is a major driver of morbidity and mortality worldwide, disproportionately impacting resource-limited settings such as sub-Saharan Africa. There are approximately 39.9 million people living with HIV (PLWH) as of 2023 and HIV is responsible for 630,000 annual deaths worldwide, including 260,000 in eastern and southern Africa [1]. Antiretroviral therapy (ART) taken for HIV treatment can extend life expectancy, reduce HIV-associated morbidity, and limit HIV transmission. ART can also be taken as pre-exposure prophylaxis (PrEP), a key biomedical strategy to prevent HIV acquisition. However, ART taken for treatment or prevention carries some risk of toxicity, requires strict adherence, and is vulnerable to emerging drug resistance that could limit its efficacy [2–4]. Moreover, poor HIV-related knowledge and unfavorable socioeconomic determinants of health are barriers to ART accessibility and adherence in sub-Saharan Africa [5–9]. By conferring durable immunity to inoculated individuals, a one-time or low-frequency preventive HIV vaccine would reduce toxicity and morbidity, decrease the emergence of drug resistance, and mitigate barriers to PrEP adherence [10].
Efficacy testing of a preventive HIV vaccine will require the recruitment and retention of behaviorally vulnerable volunteers who are willing to adhere to the conditions of study participation. Several factors may influence such participation. For example, prior knowledge of vaccine trials has been shown to positively correlate with willingness to participate [11, 12]. Barriers to participation may include the length of study participation, requirements to delay pregnancy, large blood draws, and the possibility of receiving a placebo [13]. However, differences in study population characteristics between prior studies and ours necessitate targeted evaluation of willingness to participate. Understanding barriers and facilitators to clinical trial participation can inform recruitment strategies for future efficacy testing of a candidate HIV vaccine or similar biomedical prevention interventions.
Kenya is well-poised to conduct clinical trials of novel interventions to prevent HIV, including a candidate HIV vaccine. Kenya is the 7th largest country in Africa by population with an HIV prevalence of 3.7% (1.4 million people) as of 2022, with prevalence among women (4.9%) nearly double that of men (2.4%) aged 15–49 years [14]. The country has robust research infrastructure with multiple institutions that have established strong working relationships with local county health facilities that serve key demographics vulnerable to HIV acquisition, such as female sex workers, men who have sex with men (MSM), and adolescent girls and young women [15–17]. The HIV prevalence in Kisumu County in Western Kenya is over 17% – about three times the national average – and HIV incidence is 6.9 cases per 100 person-years [18]. Future clinical trials of a preventive HIV vaccine candidate would be facilitated by a thorough understanding of factors that motivate or discourage participation by members of communities with a high burden of HIV in Western Kenya.
The RV393 protocol was developed to evaluate HIV epidemiology in Western Kenya. By drawing participants from a pool of volunteers that met the likely sociobehavioral requirements for a future clinical trial of a preventive HIV vaccine candidate, the protocol was well-positioned to characterize attitudes regarding clinical trial participation. We hypothesized that willingness to participate in this region was high, especially among people with behaviors known to be associated with HIV acquisition. The analyses described in this manuscript assessed the willingness of people without HIV (PLWOH) to participate in a hypothetical clinical trial of a preventive HIV vaccine candidate in Kisumu County, Kenya.
Methods
Study design and setting
The RV 393 cohort study was conducted in Kisumu, Kenya, to determine HIV incidence and inform future HIV vaccine clinical trials [19, 20]. From February 2017 to May 2018, the cohort recruited PLWOH who were aged 18–35 years; reported two or more sex partners in the preceding three months [21]; understood either English, Kiswahili, or Luo; intended to reside in Kisumu County for the 24-month study duration and were willing to be followed during that time; and were willing and able to give informed consent, undergo HIV testing, and provide contact information for themselves and one other person who could account for their whereabouts. A smaller subgroup of people with HIV who satisfied other inclusion criteria were recruited to mask the HIV status of enrollees, decreasing the likelihood of prospective participants being subjected to HIV-related stigma due to an inferred HIV status by observers [22]. Participants with HIV received serial viral load and CD4 T-cell count quantification as well as testing for other infectious diseases over 24 months of follow-up; this included access to diagnostic testing that was not routinely available for clinical care outside the study. Exclusion criteria included pregnancy; medical, psychiatric, or social conditions deemed likely to interfere with safety or adherence to study procedures; and current or past participation in an HIV prevention study with receipt of a therapeutic intervention. Recruitment methods included community outreach efforts via community-based organizations, beach management units, and community leaders. Targeted recruitment activity also took place at bars, markets, fishing villages, and healthcare centers, which are known foci of activity associated with HIV risk [23–27].
All participants provided written informed consent in English, Kiswahili, or Luo prior to enrollment. Participants who were illiterate underwent the consent process in the presence of an impartial witness. The study protocol was approved by institutional review boards at the Walter Reed Army Institute of Research in Silver Spring, Maryland, USA; the Kenya Medical Research Institute in Nairobi, Kenya; and all collaborating institutions.
Study procedures
Prospective participants underwent an initial screening visit where they provided demographic characteristics, completed sociobehavioral questionnaires, underwent a medical examination, and underwent HIV testing using the First Response ® Rapid HIV-1–2-0 card (Premier Medical Corporations, Maharashtra, India) as per the national guidelines algorithm [28, 29]. The GenScreen ULTRA HIV Ag-Ab Combo Kit was used in cases of inconclusive rapid tests and HIV diagnoses were confirmed with the Genius HIV-1/2 Supplemental Assay (Bio-Rad Laboratories, Hercules, CA) [30]. Eligible participants were offered enrollment and followed every three months for a maximum of 24 months. Follow-up visits included targeted medical histories, physical examinations, and serial HIV testing. Individuals found to be living with HIV were provided appropriate post-test counseling and referred to local care.
Data collection
Data for these analyses were collected via questionnaires administered by trained study staff at screening for study eligibility, enrollment, and at completion of 24 months of follow-up (see supplementary materials). The questionnaires were adapted from tools used in prior HIV cohort studies and modified for local relevance, though not formally validated. Independent variables included sociodemographic characteristics and sexual behaviors selected based on prior knowledge of factors associated with HIV acquisition risk in the region [21, 31]. Enrolled participants who acquired HIV during the 24-month study period or were lost to follow up did not complete the 24-month questionnaires. All questionnaire items allowed participants to respond with “do not know” or “refuse to answer.”
Participants were provided the following prompt about HIV vaccine clinical trials: “Clinical trials are studies performed with human subjects to test new vaccines, new drugs or new devices. Clinical trials are used to determine whether these new biomedical interventions are safe and effective. For example, when we have a candidate HIV vaccine, we would test it experimentally in a controlled environment first. This process is called a clinical trial.” Willingness to participate in a future HIV vaccine trial was ascertained by asking “Would you be willing to participate in such a study to test an experimental HIV vaccine?” Participants who responded in the negative were asked to identify one or more reasons for not wanting to participate in an HIV vaccine trial from a list provided to them. All participants were asked to identify any personal advantages that they associated with participation in an HIV vaccine trial. All participants were also asked, “How likely or unlikely would you be to enroll in a research study of a new experimental vaccine if…” and provided a list of study design characteristics. Response options included a 4-point Likert scale of “very unlikely,” “somewhat unlikely,” “somewhat likely,” and “very likely,” as well as the “do not know” and “refuse to answer” responses.
Vaccine knowledge was also assessed by soliciting a “true” or “false” response to the statement, “Can you tell by looking at someone if they have HIV?” Participants were also asked whether they had previously received information on HIV vaccine research and, if answered in the affirmative, about the source(s) of this information. We reported only enrolled participants’ responses to source(s) of information and personal advantages to participation as this population most closely resembled the target population for future HIV vaccine trial recruitment.
Statistical analyses
Participants who were known to be living with HIV at the time of screening for study eligibility were excluded from these analyses, since they would not be eligible for participation in a future preventive HIV vaccine trial. Analyses included only the participants who responded to the question about willingness to participate in a future HIV vaccine trial; participants who skipped this question or marked “do not know” or “refuse to answer” were excluded. Analyses were conducted in both the screened population and the enrolled population. The screened population provided greater statistical power for these analyses and included many viable candidates for an HIV vaccine trial who for various reasons did not meet RV393 eligibility criteria or declined to enroll in the longitudinal cohort. The enrolled population most closely matched the characteristics of a population likely to be recruited into a future preventive HIV vaccine trial based on eligibility criteria that were selected to identify individuals with heightened vulnerability to HIV acquisition.
Data on participant characteristics at screening for study eligibility were used as independent variables in these analyses. Quantitative characteristics such as age, income, and number of sexual partners were stratified into binary categories by cutoff values based on prior knowledge of factors associated with HIV acquisition risk in the region [21, 31]. Nominal and ordinal categorical characteristics were condensed into binary or trinary categories based on a priori knowledge of associations with HIV acquisition. For example, occupations were grouped into categories that included sex workers, fisherman/fishmongers, and bar/pub/restaurant workers because these occupations are known to be associated with transactional sex in the region [25, 32]. Condom use practices were categorized into “consistent” based on a response of “always,” “not consistent” based on responses of “sometimes” or “never,” and “not applicable” based on reporting no sexual partner. Male participants who reported any sex with male partners in the preceding 3 months were categorized as MSM for these analyses. Finally, chi-square or Fisher’s exact tests, based on expected cell count size, were used to compare proportions of participants who expressed willingness to participate in a future HIV vaccine trial at the screening study visit across sociodemographic and behavioral parameters of interest.
Among enrolled participants who completed the study and answered the question about willingness to participate at both screening and exit, the proportion expressing willingness to participate at screening was compared to the proportion at exit (pre-/post- analysis) using McNemar’s test.
Among participants who were unwilling to participate in a future HIV vaccine trial, reasons for being unwilling were tallied. Among all participants, potential advantages of participating in an HIV vaccine trial, likelihood of participating in an HIV vaccine trial based on various hypothetical study design elements, and sources of information regarding HIV vaccine research were tallied.
All analyses were conducted in SAS v9.4. P-values less than 0.05 were considered statistically significant and p-values less than 0.20 were considered hypothesis-generating and worthy of further investigation, acknowledging the limitation of small sample sizes for some participant characteristics [33]. Participants with missing data were excluded from statistical analyses if missing responses constituted less than 5% of total responses.
Results
Screened population
Of 1072 participants screened for study eligibility, 940 participants without previously-diagnosed HIV had valid responses to questions about willingness to participate and were included in analyses of the “screened population.” This population had a median age of 24 years (interquartile range [IQR]) 21–28) and 440 (46.8%) were female (Table 1). Of these respondents, 919 (97.8%) reported willingness to participate in a future HIV vaccine trial. Individuals who were willing to participate were more likely than those who were not to have exchanged sex for goods or money (60.1% vs. 35.0%, p = 0.0237) and less likely to have answered “yes” to the question “Can you tell by looking at someone if they have HIV?” (8.7% vs. 23.8%, p = 0.0175). Data suggested that individuals who were willing to participate may be more likely to report employment linked to high HIV risk (53.3% vs. 38.1%, p = 0.1684), to have had more than one sexual partner in the last three months (78.8% vs 65.0%, p = 0.1379), to report consistent condom use with primary sexual partners (44.2% vs. 25.0%, p = 0.1856), and to report consistent condom use with secondary sexual partners (41.6% vs. 25.0%, p = 0.1856). Willingness to participate did not vary significantly by age, sex, income, or educational attainment.
Table 1.
Demographic and other characteristics of participants screened for enrollment into an HIV incidence study in Kisumu, Kenya, stratified by self-reported willingness to participate in a potential future HIV vaccine trial
| Parameter | Overall n = 940 (%) | Unwilling to Participate n = 21 (%) | Willing to Participate n = 919 (%) | P-value | Risk Difference (95% CI) |
|
|---|---|---|---|---|---|---|
| Age | 18 to 25 years | 482 (51.3) | 11 (52.4) | 471 (51.3) | 0.9184 | |
| 26 to 35 years | 458 (48.7) | 10 (47.6) | 448 (48.7) | 0.00 (−0.02, 0.02) | ||
| Sex | Male | 500 (53.2) | 11 (52.4) | 489 (53.2) | 0.9400 | |
| Female | 440 (46.8) | 10 (47.6) | 430 (46.8) | −0.00 (−0.02, 0.02) | ||
| Income | < = 5000KSH | 271 (28.8) | 7 (33.3) | 264 (28.7) | 0.6450 | |
| > 5000KSH | 669 (71.2) | 14 (66.7) | 655 (71.3) | 0.00 (−0.02, 0.03) | ||
| Marital Status | Single | 585 (62.2) | 14 (66.7) | 571 (62.1) | 0.6717 | |
| Married, Separated, Divorced | 355 (37.8) | 7 (33.3) | 348 (37.9) | 0.00 (−0.01, 0.02) | ||
| Education | Below secondary | 394 (41.9) | 8 (38.1) | 386 (42.0) | 0.7198 | |
| Secondary and Above | 546 (58.1) | 13 (61.9) | 533 (58.0) | −0.00 (−0.02, 0.02) | ||
| Employment Status | High Risk* | 497 (52.9) | 8 (38.1) | 489 (53.3) | 0.1684 | |
| Less Risk | 442 (47.1) | 13 (61.9) | 429 (46.7) | −0.01 (−0.03, 0.01) | ||
| Missing | 1 (0.1) | - | 1 (0.1) | |||
| Exchanged Sex for Goods or Money | No | 379 (40.4) | 13 (65.0) | 366 (39.9) | 0.0237 | |
| Yes | 558 (59.6) | 7 (35.0) | 551 (60.1) | 0.02 (0.00, 0.04) | ||
| Missing | 3 (0.3) | 1 (4.8) | 2 (0.2) | |||
| Ever Had Partner with HIV | Yes | 316 (33.9) | 8 (40.0) | 308 (33.8) | 0.7441 | |
| No | 90 (9.7) | 2 (10.0) | 88 (9.7) | 0.00 (−0.03, 0.04) | ||
| Don’t Know | 525 (56.4) | 10 (50.0) | 515 (56.5) | 0.01 (−0.01, 0.03) | ||
| Missing | 9 (1.0) | 1 (4.76) | 8 (0.9) | |||
| Self-identified as Man who has Sex with Men (Male Respondents) | Not MSM | 440 (88.0) | 11 (100.0) | 429 (87.7) | 0.3759 | |
| MSM | 60 (12.0) | 0 (0.0) | 60 (12.3) | 0.03 (0.01, 0.04) | ||
| Consistent Condom Use with Primary Sexual Partner | N/A – No partner | 448 (47.9) | 12 (60.0) | 436 (47.6) | 0.1332 | |
| Not Consistent | 78 (8.3) | 3 (15.0) | 75 (8.2) | −0.01 (−0.06, 0.03) | ||
| Consistent | 410 (43.8) | 5 (25.0) | 405 (44.2) | 0.01 (−0.00, 0.03) | ||
| Missing | 4 (0.4) | 1 (4.8) | 3 (0.3) | |||
| Consistent Condom Use with Secondary Sexual Partner | N/A – No partner | 146 (15.6) | 6 (30.0) | 140 (15.3) | 0.2074 | |
| Not Consistent | 402 (42.9) | 7 (35.0) | 395 (43.0) | 0.02 (−0.01, 0.06) | ||
| Consistent | 390 (41.6) | 7 (35.0) | 383 (41.7) | 0.02 (−0.01, 0.06) | ||
| Missing | 2 (0.2) | 1 (4.8) | 1 (0.1) | |||
| Believes one can Tell a Person’s HIV Status by Looking | No | 851 (90.9) | 16 (76.2) | 835 (91.3) | 0.0348 | |
| Yes | 85 (9.1) | 5 (23.8) | 80 (8.7) | −0.04 (−0.09, 0.01) | ||
| Missing | 4 (0.4) | - | 4 (0.4) | |||
| Number of Sexual Partners in Last 3 Months | 0 or 1** | 202 (21.5) | 7 (35.0) | 195 (21.2) | 0.3236 | |
| 2 to 5 | 487 (51.9) | 8 (40.0) | 479 (52.1) | 0.02 (−0.01, 0.05) | ||
| 6 or more | 250 (26.6) | 5 (25.0) | 245 (26.7) | 0.01 (−0.02, 0.05) | ||
| Missing | 1 (0.1) | 1 (4.8) | - | |||
Pearson’s Chi-square test used for all p-values or, in cases with small cell sizes, Fisher’s exact test. All data are presented as n (column %). Reported percentages and statistical analyses excluded “missing” responses from denominator if these responses constituted less than 5% of total column responses. Statistically significant p-values (p ≤ 0.05) are in bold.
*High risk occupations included bartending, market vending, fishermen, and healthcare jobs
**2 or more sexual partners was an inclusion criterion for RV393 enrollment
Enrolled population
A total of 671 participants were enrolled, of which 619 were PLWOH, including 618 with a valid response to the question about willingness to participate in a future HIV vaccine trial. These 618 enrolled participants had a median age of 24 years (IQR 21–28) and 271 (46.5%) were female (Table 2). A total of 608 (98.4%) reported willingness to participate in a future HIV vaccine trial. Willingness to participate did not vary significantly by any participant characteristic. However, several characteristics were determined to be hypothesis-generating and warrant further investigation (p < 0.20). A greater percentage of willing participants were aged 26–35 years than were unwilling participants (46.5% vs. 20.0%, p = 0.1171), a lower proportion of willing participants completed secondary school or above (59.2% vs. 90.0%, p = 0.0557), and willing participants were more likely to report consistent condom use with their primary sexual partner (43.7% vs. 10.0%, p = 0.0722).
Table 2.
Demographic and other characteristics of participants enrolled into an HIV incidence study in Kisumu, Kenya, stratified by self-reported willingness to participate in a potential future HIV vaccine trial
| Parameter | Overall, n = 618 (%) | Unwilling to Participate n = 10 (%) | Willing to Participate n = 608 (%) | P-value | Risk Difference (95% CI) |
|
|---|---|---|---|---|---|---|
| Age | 18 to 25 years | 333 (53.9) | 8 (80.0) | 325 (53.5) | 0.1171 | |
| 26 to 35 years | 285 (46.1) | 2 (20.0) | 283 (46.5) | 0.02 (−0.00, 0.04) | ||
| Sex | Male | 341 (55.2) | 4 (40.0) | 337 (55.4) | 0.3558 | |
| Female | 277 (44.8) | 6 (60.0) | 271 (44.6) | −0.01 (−0.03, 0.01) | ||
| Income | < = 5000KSH | 160 (25.9) | 2 (20.0) | 158 (26.0) | 0.9999 | |
| > 5000KSH | 458 (74.1) | 8 (80.0) | 450 (74.0) | −0.00 (−0.03, 0.02) | ||
| Marital Status | Single | 399 (64.6) | 8 (80.0) | 391 (64.3) | 0.5069 | |
| Married, Separated, or Divorced | 219 (35.4) | 2 (20.0) | 217 (35.7) | 0.01 (−0.01, 0.03) | ||
| Education | Below secondary | 249 (40.3) | 1 (10.0) | 248 (40.8) | 0.0557 | |
| Secondary and Above | 369 (59.7) | 9 (90.0) | 360 (59.2) | −0.02 (−0.04, −0.00) | ||
| Employment Status | High Risk* | 302 (48.9) | 3 (30.0) | 299 (49.3) | 0.3408 | |
| Less Risk | 315 (51.1) | 7 (70.0) | 308 (50.7) | −0.01 (−0.03, 0.01) | ||
| Missing | 1 (0.16) | - | 1 (0.16) | |||
| Exchanged Sex for Goods or Money | No | 174 (28.2) | 4 (40.0) | 170 (28.0) | 0.4793 | |
| Yes | 443 (71.8) | 6 (60.0) | 437 (72.0) | 0.01 (−0.02, 0.03) | ||
| missing | 1 (0.16) | - | 1 (0.16) | |||
| Ever Had Partner with HIV | Yes | 147 (23.9) | 2 (20.0) | 145 (24.0) | 0.9999 | |
| No | 74 (12.1) | 1 (10.0) | 73 (12.1) | 0.00 (−0.03, 0.03) | ||
| Don't Know | 393 (64.0) | 7 (70.0) | 386 (63.9) | −0.00 (−0.03, 0.02) | ||
| Missing | 4 (0.65) | - | 4 (0.66) | |||
| Self-identified as Man who has Sex with Men (Male respondents) | Not MSM | 293 (47.4) | 4 (40.0) | 289(47.5) | 0.999 | |
| MSM | 48 (7.8) | 0 (0.0) | 48(7.9) | 0.01 (0.00, 0.03) | ||
| Consistent Condom Use with Primary Sexual Partner | N/A – No partner | 303 (49.1) | 8 (80.0) | 295(48.6) | 0.0722 | |
| Not Consistent | 48 (7.8) | 1 (10.0) | 47(7.7) | 0.01 (−0.04, 0.05) | ||
| Consistent | 266 (43.1) | 1 (10.0) | 265(43.7) | 0.02 (0.00, 0.04) | ||
| Missing | 1 (0.16) | - | 1 (0.16) | |||
| Consistent Condom Use with Secondary Sexual Partner | N/A – No partner | 4 (0.6) | 0 (0.0) | 4(0.7) | 0.3823 | |
| Not Consistent | 312 (50.6) | 7 (70.0) | 305(50.2) | −0.02 (−0.04, −0.01) | ||
| Consistent | 301 (48.8) | 3 (30.0) | 298(49.1) | −0.01 (−0.02, 0.00) | ||
| Missing | 1 (0.16) | - | 1 (0.16) | |||
| Believes one can Tell a Person’s HIV Status by Looking | No | 565 (91.9) | 9 (90.0) | 556(91.9) | 0.5745 | |
| Yes | 50 (8.1) | 1 (10.0) | 49(8.1) | −0.00 (−0.04, 0.04) | ||
| Missing | 3 (0.49) | - | 3 (0.49) | |||
| Number of Sexual Partners | 2 to 5 | 408 (66.0) | 6 (60.0) | 402(66.1) | 0.7408 | |
| 6 or more | 210 (34.0) | 4 (40.0) | 206(33.9) | −0.00 (−0.03, 0.02) | ||
Fisher’s exact test was used for all p-values. All data are presented as n (%). Reported percentages and statistical analyses excluded “missing” responses from denominator if these responses constituted less than 5% of total column responses.
*High risk occupations included bartending, market vending, fishermen, and healthcare jobs
Exit population
Of 618 enrolled PLWOH who answered the question about willingness to participate in a future HIV vaccine trial, 533 (86.2%) completed an exit questionnaire after 24 months of follow-up. The median age at enrollment of the exit population was 24 years (IQR 21–28) and 280 (44.4%) were female. At study exit, 518 participants (97.2%) were willing to participate in a future HIV vaccine trial, including 7 participants who were previously unwilling at enrollment. However, 12 participants who expressed willingness to participate at enrollment subsequently expressed unwillingness at study exit. The reasons for these shifts in willingness were not assessed.
Sources of information
Of the 618 participants enrolled, the vast majority had received information about HIV vaccine research from radio/television (n = 608, 98.1%) and newspapers/brochures/magazines (n = 579, 93.1%). The participants who cited these sources vastly outnumbered those citing other sources such as friends/relatives (n = 56, 9.2%), the Internet (n = 46, 7.6%), non-governmental organizations (n = 37, 6.1%), and health workers (n = 2, 0.3%). There were no statistically significant differences in sources of information between people who were willing and unwilling to participate in a future HIV vaccine trial.
Facilitators and barriers to willingness to participate
Participants were presented with potential advantages of future HIV vaccine trial participation reflected in Fig. 1. Potential advantages that were identified by the 618 enrolled participants included learning how to avoid risky behavior (n = 592, 95.8%), receiving regular health care related to research (n = 576, 93.2%), and receiving free HIV counseling and testing (n = 574, 92.8%). Fewer participants cited receiving reimbursement for participation as an advantage (n = 502, 81.2%). Among 271 female participants, 235 (87.0%) identified receiving free pregnancy tests every three months as an advantage to participation.
Fig. 1.
Incentives for HIV vaccine trial participation. Participants were presented with personal advantages of participating in an HIV vaccine trial and asked to select all that applied. Percentages were calculated using 618 enrolled participants as a denominator with the exception of pregnancy testing which used the 271 enrolled females.
Participants were also presented with theoretical future HIV vaccine trial characteristics reflected in Fig. 2. The majority of the 618 enrolled participants reported being very or somewhat likely to participate (n = 608, 98.4%). A study requirement for HIV testing every 3 months produced a high proportion of “very likely” responses among the 608 willing participants (n = 600, 98.7%). However, some willing participants expressed being very or somewhat unlikely to participate if they were required to receive injections of multiple vaccine candidates (n = 25, 4.0%), an effect amplified among the 10 unwilling participants (n = 9, 90.0%). Among 271 female participants, 28 (10.4%) were very or somewhat unlikely to participate if required to use family planning such as hormonal contraception during a future HIV vaccine trial.
Fig. 2.
Willingness to enroll based on hypothetical attributes of HIV vaccine trial. Participants were presented with attributes of a hypothetical HIV vaccine study and asked to indicate their likelihood of participation on a 4-point Likert scale. For each attribute, responses were stratified by willingness (WTP) and non-willingness to participate (nWTP).
Among the 10 enrolled participants who were unwilling to participate in a future HIV vaccine trial at study entry, five (50.0%) cited a fear of acquiring HIV, five (50.0%) cited a fear of side effects, and three (30.0%) cited a fear of needlesticks. One (10.0%) cited each of the following reasons: fear of testing positive for HIV, time required for study visits, partner refusal to let them participate, and someone else would decide about participation. Nobody reported fear of death or fear of fetal abnormalities as reasons for being unwilling to participate.
Discussion
Our study demonstrated a high level of willingness to join a future HIV vaccine trial among participants in Kisumu County, Kenya, with nearly all screened and enrolled individuals expressing interest. Among individuals screened for study eligibility, willingness to participate was more common among those who had exchanged goods for sex but less common among those with misconceptions about HIV. Receipt of HIV-related information occurred predominantly from public media outlets rather than research and healthcare professionals. Moreover, female participants were potentially deterred by a requirement to use contraception during a future HIV vaccine trial.
Almost all participants in our study expressed willingness to participate in a future HIV vaccine trial. This is similar to what has been observed in other East African communities with sexual risk for HIV acquisition, such as a Ugandan fishing community where 99.4% of individuals were willing to participate in a future HIV vaccine trial [13] and a study of Kenyan MSM and female sex workers where 81.3% were willing to participate [34]. In contrast, cohorts of urban residents who injected drugs showed less willingness to participate, as in Tanzania (50.6%) and China (74.3%) [12, 35]. Moreover, just 60.0% of an MSM cohort in German urban centers were willing to participate [36]. These differences demonstrate how population characteristics may influence willingness to participate and underscore the need for context-specific formative research and community engagement to improve recruitment of target populations.
Our data suggest that people who exchange goods for sex may be more willing to participate in an HIV vaccine trial while people with misconceptions about HIV may be less willing to participate. Transactional sex was associated with willingness to participate in a Ugandan fishing community that had similar demographics and HIV risk factors to our study [13, 37]. A Kenyan cohort of female sex workers also demonstrated high willingness to participate[34]. It is possible that transactional sex is a well-recognized risk factor for HIV and self-perception of risk motivates interest in an HIV vaccine trial. We have previously shown that people who engage in transactional sex are a heterogenous group and differentiated interventions may be needed to recruit and retain them in future HIV vaccine trials [38]. Correcting misconceptions about HIV through educational activities may also improve willingness to participate in a future HIV vaccine trial, though some prior studies have not shown a strong relationship between HIV knowledge and willingness to participate [11, 13]. Fear of acquiring HIV from a vaccine and fear of side effects—two major reasons for unwillingness to participate that were cited by participants in our study—could be proactively addressed through community engagement and educational campaigns.
A small number of individuals who completed the study changed their answer to the question of willingness to participate in a future HIV vaccine trial. While we did not assess factors that correlated with these shifts, these findings suggest that vaccine attitudes are fluid, and that regular monitoring would help identify regions of waning interest and acceptance [39]. Future research should investigate sources of negative sentiments towards trial participation and inform interventions to attenuate them.
Sources of information about HIV vaccine research in our population were overwhelmingly skewed towards radio/TV and newspapers/brochures/magazines, and away from research centers and medical providers. While the sustained HIV research activity in western Kenya may have boosted general awareness, this trend suggests a gap in communication between HIV investigators and target populations. Recent examples of COVID-19 vaccine trial recruitment demonstrate how researchers liaising directly with target communities, rather than relying on media sources, can play a crucial role in trust-building and recruitment [40]. In our population, leveraging existing surveillance platforms that periodically engage with local communities may help research centers disseminate reliable information on HIV and HIV-related research [41]. Radio, television, and print media may be suitable venues for broad educational campaigns to correct misconceptions around HIV and vaccines.
In our study, protection from HIV, self-education on HIV topics, and receiving healthcare benefits were among the factors that incentivized willingness to participate in a future HIV vaccine trial. Similar observations have been recorded in other studies [13, 35–37, 42]. These themes suggest a benefit to integrating research into broader clinical settings with access to education, diagnostic testing, other prevention tools, and therapeutics [40]. Moreover, while few participants in our study cited monetary reimbursement as an incentive, the possibility of underlying self-serving biases is not excluded. Trial organizers should ensure fair compensation for participants while avoiding overcompensating participants to the degree that financial incentives become a primary motivator for participation.
A notable minority of female participants in our study would be unlikely to participate in a future HIV vaccine trial if required to use contraception to prevent. Contraception is a frequent requirement of early-phase clinical trials in order to mitigate risk of fetal abnormalities induced by the investigational product. Access to effective contraception and knowledge of its purpose should be assessed in any preparatory study for HIV vaccine trials. Integrating family planning counseling into trial sites and providing contraceptive resources for participants is ethically necessary.
Our study had several limitations. First, willingness to participate was hypothetical as no specific details about future HIV vaccine trials were provided when participants were asked about their willingness; as has been observed in prior studies, it is possible that response to this single question overestimates the population’s true recruitment rate when an HIV vaccine study does become available [43]. Second, only unwilling participants were asked about reasons why they were unwilling, thus we did not capture sources of hesitancy that may exist even among participants who expressed willingness. Third, as only 10 participants expressed unwillingness to participate at enrollment, there was too little variability in this outcome to perform multivariate modeling of factors associated with willingness to participate. Fourth, our questionnaires were not designed to assess reasons behind attitude shifts for participants who subsequently changed their answers to the question of “willingness to participate.” Fifth, sociodemographic and behavioral data were mostly collected via self-report using data collection instruments that were not formally validated; this may have introduced recall and other biases while also limiting comparability to data from other studies. Sixth, an unexpectedly high frequency of participants reported being very or somewhat unlikely to participate if the research center were open on the weekends, suggesting perhaps a misunderstanding that participants would be required to present on weekends, as opposed to simply having the option to do so; a follow-up qualitative assessment via interviews may help explain this unexpected finding. Last, the impact of the COVID-19 pandemic on vaccine literacy and attitudes was not captured in this study. Subsequent studies in the post-pandemic era would better contemporize our findings.
In summary, we identified a cohort of potential study volunteers in western Kenya with high willingness to participate in future testing of HIV prevention interventions such as a candidate vaccine. However, we also identified barriers to participation in our population that include gaps in HIV-related knowledge and certain vaccine trial requirements. Successful recruitment into HIV vaccine trials will require continual engagement of future participants to address concerns and misconceptions regarding research of this nature.
Supplementary Information
RV393 HIV Behavior Risk Assessment Questionnaire (Follow-Up).
RV393 HIV/AIDS Awareness, Vaccine Knowledge and Willingness to Participate Questionnaire.
RV393 HIV Behavior Risk Assessment Questionnaire (Screening).
Acknowledgements
We acknowledge Mr. Peter Sifuna of the Kombewa Clinical Research Center for providing the Health and Demographic Surveillance System platform for study recruitment and data collection. We also acknowledge Dr. Kyle Petersen and Dr. Martin Ottolini of the Uniformed Services University of the Health Sciences for facilitating the primary author’s visits to collaborating sites in Kenya. The authors are also thankful to the study participants who made this work possible. Institutions that supported this work included the Kenya Medical Research Institute (KEMRI), Henry M. Jackson Foundation for the Advancement of Military Medicine (HJF), HJF Medical Research International (HJFMRI), US Military HIV Research Program (MHRP), Walter Reed Army Institute of Research (WRAIR), WRAIR-Africa, and theh Kenya Ministry of Health. In addition to the masthead authors of this manuscript, the RV393 Study Group includes: Rachel Adongo, Rachel Aguttu, Hosea Akala, Julie Ake, Michael Bondo, Erica Broach, Christine Busisa, Nate Copeland, Jessica Cowden, Mark de Souza, Leigh Anne Eller, Milicent Gogo, Tyler Hamby, Zebiba Hassen, Dale Hu, Michelle Imbach, Anne Juma, Oscar Kasera, Qun Li, Margaret Mbuchi, Mark Milazzo, Kayvon Modjarrad, Eric Ngonda, Jacob Nyariro, Jew Ochola, Roseline Ohore, Thomas Okumu, Mary Omondi, Linnah Ooro, Beatrice Orando, Victorine Owira, Roselyn Oyugi, Eric Rono, Valentine Sing’oei, Chi Tran, Hannah Turley.
Disclaimer
Material has been reviewed by the Walter Reed Army Institute of Research. There is no objection to its presentation and/or publication. The opinions or assertions contained herein are the private views of the author, and are not to be construed as official, or as reflecting true views of the Department of the Army or the Department of Defense. The investigators have adhered to the policies for protection of human participants in research as prescribed in Army Regulation 70–25.
Authors’ contributions
Conceptualization – Joseph Tang, Merlin L. Robb, Christina S. Polyak, Trevor A. Crowell; Formal analysis—Adam Yates; Funding acquisition—Merlin L. Robb; Investigation—John Owuoth, Valentine Sing’oei, June Otieno, Hezekiah Odongo, Jacob Nyariro, Kennedy Otieno; Project administration—Chiaka Nwoga, Christina S. Polyak; Supervision—Trevor A. Crowell, Christina S. Polyak, Patrick W. Hickey; Visualization—Joseph Tang; Writing—original draft—Joseph Tang; Writing—review & editing—All authors.
Funding
This work was supported by agreements (W81XWH-11–2-0174; W81XWH-18–2-004; HT9425-24–3-0004) between the Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc., and the U.S. Department of Defense. This research was funded, in part, by the U.S. National Institute of Allergy and Infectious Diseases and the Infectious Diseases Society of America.
Data availability
To request a minimal data set, please contact the Data Coordinating and Analysis Center (DCAC) at PubRequest@hivresearch.org and indicate the RV393 study along with the name of the manuscript.
Declarations
Ethics approval and consent to participate
The RV393 study was reviewed and approved by the Kenya Medical Research Institute Scientific and Ethical Review Unit, Nairobi, Kenya and the Walter Reed Army Institute of Research Institutional Review Board, Silver Spring, Maryland USA. The study was conducted in accordance with the principles described in the International Conference on Harmonization Good Clinical Practice guidelines, the Nuremberg Code, the Belmont Report, the Declaration of Helsinki, and federal regulations regarding the protection of human participants as described in 32 CFR 219 and Army Regulation 70–25. All participants and impartial witnesses of illiterate participants provided written informed consent before screening for study eligibility.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
RV393 HIV Behavior Risk Assessment Questionnaire (Follow-Up).
RV393 HIV/AIDS Awareness, Vaccine Knowledge and Willingness to Participate Questionnaire.
RV393 HIV Behavior Risk Assessment Questionnaire (Screening).
Data Availability Statement
To request a minimal data set, please contact the Data Coordinating and Analysis Center (DCAC) at PubRequest@hivresearch.org and indicate the RV393 study along with the name of the manuscript.