HPV16/18 antibodies 16-years after single dose of bivalent HPV vaccination: Costa Rica HPV vaccine trial

Abstract

Background

The Costa Rica HPV Vaccine Trial provided initial evidence that 1 dose of the bivalent human papillomavirus (HPV) vaccine induces stabilizing antibody levels that may provide extended protection against HPV-16/18 infections. We report antibody seropositivity and stability 11 to 16 years after vaccination.

Methods

We invited a random subset of Costa Rica HPV Vaccine Trial participants (n = 398) who had received 3 doses and all women (n = 203) who had received 1 dose at 18 to 25 years of age to follow-up visits 11, 14, and 16 years after vaccination. We calculated HPV-16 and HPV-18 seropositivity and assessed change in enzyme-linked immunosorbent assay antibody levels 11 to 16 years after vaccination among 500 participants.

Results

By year 16, 99.4% (95% confidence interval [CI] = 96.8% to 100.0%) and 100.0% (95% CI = 98.9% to 100.0%) of 1-dose and 3-dose recipients, respectively, were HPV-16 seropositive and 98.8% (95% CI = 95.9% to 99.9%) and 100% (95% CI = 98.9% to 100.0%) of 1-dose and 3-dose recipients, respectively, were HPV-18 seropositive. Between years 11 and 16, women who had received 3 doses had a small but statistically significant decrease in the geometric mean concentration for HPV-16 of ‒12.4% (95% CI = ‒16.3% to ‒8.4%) and HPV-18 of ‒13.4% (95% CI = ‒17.2% to ‒9.4%). Among women who had received 1 dose, the decrease was statistically significant for HPV-16 at ‒8.9 (95% CI = ‒14.2% to ‒3.1%) but nonsignificant for HPV-18. Geometric mean concentration ratios of 3:1 dose (year 16) were 3.0 and 2.2 for HPV-16 and HPV-18, respectively.

Conclusions

HPV-16/18 seropositivity remained exceedingly high 16 years after vaccination. Over 5 years, small declines in antibodies were observed. Women should have protection for at least 20 years and likely much longer at the observed rate of decline.

Human papillomavirus (HPV) vaccination is essential for reducing the rate of cervical cancer. The World Health Organization’s global strategy to accelerate cervical cancer elimination as a public health problem recommends including HPV vaccines in national programs, reaching 90% of girls by age 15 years by 2030 (1). Although 137 countries (70%) have introduced HPV vaccination, global coverage of target-aged girls is about 21%, partly because several big countries have not started or have low uptake (2). The first vaccine was licensed almost 20 years ago (2006); the slow progress in coverage has been due to the high cost of the vaccine, logistical difficulties in administering multidose vaccines in adolescents, and supply shortages.

Currently, 6 prophylactic HPV vaccines are licensed around the world. For girls aged 9 to 14 years, the main target population, these vaccines are licensed in a 2-dose schedule. In 2011, the Costa Rica HPV Vaccine Trial (CVT) provided the first evidence that a single dose of the HPV vaccine could be as protective as 3 doses. We demonstrated that a decade after vaccination, individuals who had received a single dose of the HPV vaccine had high protection against HPV-16/18 infection, as did those individuals who had received 2 or 3 doses, although antibody titers after a single dose were lower (3). In 2022, the World Health Organization reviewed evidence for single-dose HPV vaccination and now recommends an alternative single-dose schedule as an off-label option for female and male individuals aged 9 to 20 years (4). This recommendation was based on increasingly robust data suggesting strong protection by a single dose of the vaccine, paired with modeling studies indicating that 1-dose vaccination of girls yields substantial health benefits and is cost saving compared with no vaccination. One key variable driving cost-effectiveness between 1 and 2 doses is the durability of protection; modeling data indicate that if 1 dose protects against HPV-16/18 infection for at least 20 years, the second dose will not be cost-effective (5,6).

It is undocumented whether a single dose of the vaccine will provide long-term protection. The longest follow-up data come from post hoc analyses of efficacy trials of the bivalent (CVT) (3) and quadrivalent (India Trial) vaccines (7). In CVT, 11 years after initial vaccination, high efficacy against 6-month persistent HPV-16 and HPV-18 infection was observed for 1, 2, and 3 doses. Recipients of 1 dose had 4-fold lower antibody titers, but seropositivity was similar by dose group. To continue the investigation of protection by single-dose and multiple-dose HPV vaccination in CVT, all single-dose vaccine recipients and a subset of the 3-dose recipients are being followed up to 20 years after initial vaccination for immunogenicity outcomes. If antibody levels remain stable over time, we can infer that 1 dose will continue to provide the robust high vaccine efficacy observed in prior years. In this update, we report HPV-16 and HPV-18 antibody seropositivity and stability 11 to 16 years after initial vaccination among women vaccinated at ages 18 to 25 years.

Methods

Study participants and procedures

CVT was a community-based, randomized, double-blind, prelicensure, phase III trial (ClinicalTrials.gov identifier NCT00128661). The primary objective was to evaluate the efficacy of the bivalent vaccine (HPV-16/18 AS04-adjuvanted vaccine [Cervarix, GlaxoSmithKline Biologicals, Brentford, UK]) for the prevention of cervical HPV-16/18 infection and related precancerous lesions (8). Institutional review boards in Costa Rica and the United States approved the study, and participants provided written informed consent.

Between June 2004 and December 2005, 7466 healthy women between 18 and 25 years of age from 2 provinces of Costa Rica were enrolled. Women were randomly assigned (1:1) to HPV-16/18 vaccine or Havrix hepatitis A vaccine (GlaxoSmithKline Biologicals) as a control at 0, 1, and 6 months and followed up for 4 years. At the end of the 4-year blinded phase, participants were offered the vaccine they had not received at enrollment, and most in the original HPV vaccine group were invited to a long-term follow-up study (9). Participants provided blood samples, and those individuals who had initiated sexual activity underwent pelvic examinations to collect cervical cells for cytology and HPV DNA testing.

In CVT, approximately 20% of participants received fewer than 3 doses of their assigned vaccine. Reasons for missing doses were mostly pregnancy and colposcopic referral during the vaccination phase; rates were similar between women who had received HPV and control vaccines (10). We evaluated vaccine efficacy against virologic endpoints by number of doses up to 11 years, and efficacy estimates against HPV-16/18 were similar for 1, 2, and 3 doses (3). After the 11-year visit, we invited all women who had received a single dose, women who had received 2 doses, and a random sample of women who had received 3 doses to continue follow-up to 20 years, when they ranged in age from 38 to 45 years. Participants were invited to 4 follow-up visits 14, 16, 18, and 20 years after HPV vaccination. Women who agreed signed new informed consent forms. We do not report the results for the 2-dose group because most missed their 6-month visit, resulting in a 0-month and 1-month vaccination schedule, which is not recommended or used. We administered a questionnaire on sexual behavior, smoking status, contraceptive use, reproductive history, and other variables potentially affecting immune response. The clinician collected a blood sample that was stored at between 2 and 8 °C in certified cold boxes. On the day of collection, the cold boxes were transported to the local biobank, where aliquots of serum were prepared and immediately frozen at ‒80 °C until shipment under cryogenic temperatures to the US National Cancer Institute for long-term storage.

Measurement of antibodies against HPV-16 and HPV-18 by enzyme-linked immunosorbent assay

All samples from 14-year and 16-year visits for the 1-dose and 3-dose groups were analyzed blindly in the same batch along with samples from the 11-year visit to evaluate the 5-year trajectory without potential batch effects. HPV-16 and HPV-18 enzyme-linked immunosorbent assay (ELISA) testing was performed at the HPV Serology Laboratory, Frederick National Laboratory for Cancer Research (3). Briefly, polystyrene flat-bottom microtiter plates (MaxiSorp, high binding; Nunc Cell Culture, Thermo Fisher Scientific, Waltham, MA) were coated with HPV-16 virus-like particles (2.7 µg/mL) or HPV-18 virus-like particles (2.0 µg/mL) and incubated at 4 °C for 3 to 5 days. The plates were washed with phosphate-buffered saline containing 0.05% Tween 20. After blocking the plates with a buffer containing 4% skim milk and 0.2% Tween 20 in phosphate-buffered saline, the plates were washed again. Serum was initially diluted 1/100 in blocking buffer and added to the plate. Next, the 1/100 diluted serum was serially diluted in blocking buffer in 2-fold increments in the assay plate to a final dilution of 1/12 800. The plates were incubated for 1 hour at room temperature with gentle shaking. After washing the plate, a solution of peroxidase-labeled goat anti–human immunoglobulin G (KPL, Inc, Gaithersburg, MD) was added for 1 hour at room temperature with gentle shaking. After washing, the plate was developed with a tetramethylbenzidine substrate solution (KPL, Inc) for 25 minutes in the dark at room temperature. The reaction was stopped with 0.36 N sulfuric acid, and the absorbance (450-620 nm) was measured with a microtiter plate reader (SpectraMax [Molecular Devices, Sunnyvale, CA]). Antibody levels, expressed as ELISA units/mL, were calculated by interpolating optical density values from the standard curve by averaging the calculated concentrations from all dilutions that fall within the working range of the standard curve. The seropositivity cutoff of the HPV-16 assay is less than 8 ELISA units/mL, and the seropositivity cutoff of the HPV-18 assay is less than 7 ELISA units/mL. Any assay levels reported below these cutoff values are treated as seronegative. To establish the seropositive cutoff, the laboratory evaluated serum samples from 30 girls who reported never having had sex, and the 95% confidence interval (CI) of the geometric mean of the antibody concentrations was calculated for these tests. Moreover, the results were converted to IU/mL based on the following conversion factor for HPV-16 (1 IU/mL = 6.11 ELISA units/mL) and HPV-18 (1 IU/mL = 5.66 ELISA units/mL). The conversion factor was derived from testing the anti–HPV-16 (UK National Institute for Biological Standards and Control, catalog No. 05/134, 10 IU/mL) and anti–HPV-18 (catalog No. 10/140, 16 IU/mL) international standard in replicate with the laboratory’s in-house reference standard, which has an established arbitrary ELISA unit/mL concentration.

To evaluate the reproducibility of the assay, 5% of samples were randomly selected for blinded duplicate testing. The correlation between duplicate measures was 99%, and the intraclass correlation coefficient was 2%, indicating minimal variability in measurement.

Statistical analysis

All women who received 1 HPV vaccine dose and a random sample of women who received 3 doses were invited to participate in the extended follow-up (n = 601). Of these individuals, 23 (12 in the 1-dose group and 11 in the 3-dose group) were excluded. Ultimately, 578 women were enrolled, and more than 94% attended follow-up visits; participation was similar by dose group (Figure 1).

Figure 1.

CONSORT diagram of participants in the CVT included in the analytical cohort. CVT = Costa Rica HPV Vaccine Trial; HPV = human papillomavirus.

For this analysis, we excluded 32 women from the 3-dose group who had originally been invited because they had low antibody levels; we also excluded 46 women (18 in the 1-dose group and 28 in the 3-dose group) who had missed at least 1 visit. The analytical cohort included 500 women who attended the 3 visits at 11, 14, and 16 years. One woman did not have available HPV-18 serology results and was excluded.

We describe HPV-16 and HPV-18 antibodies elicited by 1 and 3 doses for each follow-up visit and the number and percentage of participants who were anti–HPV-16 and anti–HPV-18 seropositive at each visit. For antibody levels, we report the geometric mean concentration in IU/mL and 95% CIs. We present absolute and relative change in the geometric mean concentration with 95% CIs, estimated using the δ method.

To visually evaluate the shift in antibody levels, we present the cumulative distribution of HPV-16 and HPV-18 antibodies by dose group for each follow-up visit. For each woman, we calculated the percentage change in antibody levels between years 11 and 16 (level 11 ‒ level 16/level 11) and categorized them by deciles. We graphically present the percentage of women in the specified category.

A sensitivity analysis presents the results for the entire population (546 women) in Supplementary Tables and Figures (available online).

Results

Sixteen years after initial vaccination, 55% of women were between 33 and 37 years of age, and 45% were between 38 and 42 years of age. Women who had received 1 and 3 doses had a similar number of lifetime sexual partners (Supplementary Table S1, available online). The median follow-up time was 16.0 years and was the same by dose group.

Both, HPV-16 and HPV-18 seropositivity ranged from 98.8% to 100% for women who had received 1 and 3 doses at 11, 14, and 16 years after initial HPV vaccination. The lower bound of all 95% CIs for seropositivity at all time points, by dose group, and for HPV-16 and HPV-18 was 95.9%, indicating robust precision (Table 1).

Table 1.

Antibody seropositivity and geometric mean concentration for HPV-16 and HPV-18 among women who had results at the 3 time points (11-, 14-, and 16-year visit), by dose group

	1 dose of HPV vaccine			3 doses of HPV vaccine
	Seropositivity			Seropositivity
	n/N	% (95% CI)	Geometric mean concentration, IU/mL (95% CI)	n/N	% (95% CI)	Geometric mean concentration, IU/mL (95% CI)
Anti–HPV-16
11-y visit	173/173	100.0 (97.9 to 100.0)	25.2 (21.2 to 30.0)	327/327	100.0 (98.9 to 100.0)	80.3 (72.8 to 88.4)
14-y visit	171/173	98.8 (95.9 to 99.9)	24.3 (20.4 to 28.8)	327/327	100.0 (98.9 to 100.0)	74.5 (67.6 to 82.1)
16-y visit	172/173	99.4 (96.8 to 100.0)	23.0 (19.4 to 27.2)	327/327	100.0 (98.9 to 100.0)	70.2 (63.5 to 77.6)
Absolute change, IU/mLa			‒2.2 (‒3.8 to ‒0.7)			‒10.0 (‒13.4 to ‒6.5)
Relative change, %a			‒8.9 (‒14.2 to ‒3.1)			‒12.4 (‒16.3 to ‒8.4)
Anti–HPV-18
11-y visit	171/172	99.4 (96.8 to 100.0)	16.2 (13.6 to 19.4)	327/327	100.0 (98.9 to 100.0)	41.0 (36.9 to 45.5)
14-y visit	171/172	99.4 (96.8 to 100.0)	16.1 (13.5 to 19.2)	327/327	100.0 (98.9 to 100.0)	38.3 (34.5 to 42.5)
16-y visit	170/172	98.8 (95.9 to 99.9)	15.8 (13.2 to 18.9)	327/327	100.0 (98.9 to 100.0)	35.5 (31.9 to 39.6)
Absolute change, IU/mLa			‒0.4 (‒1.6 to 0.7)			‒5.5 (‒7.3 to ‒3.7)
Relative change, %a			‒2.7 (‒9.5 to 4.7)			‒13.4 (‒17.2 to ‒9.4)

^aThe absolute and relative changes in geometric mean concentration were calculated using 11-year and 16-year antibody measurements. CI = confidence interval; HPV = human papillomavirus.

The HPV-16 antibodies’ geometric mean concentration at year 11 among 1 dose recipients was 25.2 IU/mL (95% CI = 21.2 to 30.0) and at year 16 was 23.0 IU/mL (95% CI = 19.4 to 27.2). During this period, the HPV-16 geometric mean concentration had a statistically significant relative decline of 8.9% (95% CI = ‒14.2% to ‒3.1%) or a 2.2 IU/mL (95% CI = ‒3.8 to ‒0.7) absolute decline (Table 1 and Supplementary Figure S1, available online). Women who had received 3 doses had higher antibody levels; the HPV-16 geometric mean concentration at year 11 was 80.3 IU/mL (95% CI = 72.8 to 88.4) and in year 16 was 70.2 IU/mL (95% CI = 63.5 to 77.6). During this period, there was a statistically significant relative decline in HPV-16 antibody geometric mean concentration of 12.4% (95% CI = ‒16.3% to ‒8.4%) and an absolute decline of 10.0 IU/mL (95% CI = ‒13.4 to ‒6.5). Sixteen years after HPV vaccination, the ratio in the HPV-16 antibody concentration between recipients of 1 and 3 doses was 3.0.

The HPV-18 geometric mean concentration among recipients of 1 dose, measured at year 11, was 16.2 IU/mL (95% CI = 13.6 to 19.4); at year 16, it was 15.8 IU/mL (95% CI = 13.2 to 18.9). During this period, there was a non–statistically significant relative decline in the HPV-18 geometric mean concentration of 2.7% (95% CI = ‒9.5% to 4.7%) and an absolute decline of 0.4 IU/ml (95% CI = ‒1.6 to 0.7) (Table 1 and Supplementary Figure S1, available online). Women who had received 3 doses had higher HPV-18 antibody levels: at year 11, the HPV-18 geometric mean concentration was 41.0 IU/mL (95% CI = 36.9 to 45.5), and at year 16 it was 35.5 IU/mL (95% CI = 31.9 to 39.6). During this period, there was a statistically significant relative decline in HPV-18 geometric mean concentration of 13.4% (95% CI = ‒17.2% to ‒9.4%) and an absolute decline of 5.5 IU/ml (95% CI = ‒7.3 to ‒3.7). Sixteen years after HPV vaccination, the ratio in the HPV-18 antibody concentration between recipients of 1 and 3 doses was 2.2.

We visually evaluated the cumulative distribution function of HPV-16 and HPV-18 antibodies by dose group in years 11, 14, and 16. The full distribution of antibody responses appeared similar at each visit among women who had received 1 dose. Similar results were observed for recipients of 3 doses (Figure 2, A and 2, B).

Figure 2.

The cumulative distribution function of HPV-16 (A) and HPV-18 (B) antibody concentrations among women who had results at the 3 time points (11-, 14-, and 16-year visit), by dose group by year. ELISA = enzyme-linked immunosorbent assay; HPV = human papillomavirus.

In the quantitative assessment of decreases and increases in antibody concentration by decile from the 11-year to 16-year visit, for HPV-16 antibody levels, 61% and 70% of 1-dose and 3-dose recipients, respectively, had a 0% to 50% decrease in antibody concentration over the 5-year study period. Further, 22% and 17% of 1-dose and 3-dose recipients had between a 0% and 50% increase in antibody concentration. Similar results were observed for HPV-18 (Figure 3, A and 3, B).

Figure 3.

Percentage change in serum antibody level between years 11 and 16, categorized by deciles for HPV-16 (A) and HPV-18 (B), by dose group. HPV = human papillomavirus.

Because an increase in antibody levels could result from natural exposure to HPV-16 or HPV-18 (ie, anamnestic response), we investigated the HPV-16 and HPV-18 geometric mean concentration by year and dose group after excluding women with a 100% or larger increase between year 11 and year 16 (for HPV-16, 10 [5.8%] individuals who had received 1 dose and 15 [4.6%] individuals who had received 3 doses; for HPV-18, 14 (8.1%) individuals who had received 1 dose and 11 (3.3%) individuals who had received 3 doses). This analysis estimated a higher geometric mean concentration decline over the follow-up period: HPV-16 geometric mean concentration significantly decreased by 14.1% (95% CI = ‒18.5% to ‒9.6%) among women who had received 1 dose and 17.4% (95% CI = ‒20.1% to ‒14.5%) among women who had received 3 doses. The HPV-18 geometric mean concentration decreased by 10.9% (95% CI = ‒16.2% to ‒5.1%) for women who had received 1 dose and 17.2% (95% CI = ‒20.2% to ‒14.2%) for women who had received 3 doses.

In the sensitivity analysis, including women who had missed at least 1 visit (n = 546), the results were comparable to those in the analytical cohort (Supplementary Table S2, Figures S2 and S3, available online).

Discussion

We are extending our evaluation of protection by 1 and 3 doses of the bivalent HPV vaccine in CVT up to 20 years after the initial HPV vaccination. In this update, we report HPV-16 and HPV-18 antibodies 11 to 16 years after initial HPV vaccination; the 20-year visit is ongoing. We observed that 16 years after vaccination, nearly 100% of 1-dose and 3-dose recipients have remained seropositive for HPV-16 and HPV-18, and the drop in antibody concentration between 11 and 16 years was modest.

During these 5 years, the decline in HPV-16 antibodies was statistically significant regardless of the number of doses received; for HPV-18, the decline was statistically significant only among recipients of 3 doses. Although at first glance it may be concerning that antibody levels are declining over 5 years, but investigating longer periods increases the potential for statistically significant declines compared with assessments over shorter periods.

The key question is, given the observed decline, whether a loss of protection could be expected. As there is no established correlate of protection, we emphasize that most women remained seropositive 16 years after HPV vaccination. The rate of decline in antibody concentration over 5 years was approximately 10%, or 2% per year. Given the 1-dose levels observed at 16 years, we project that women will have adequate antibody levels for a minimum of 20 to 30 years after vaccination. Modeling work is ongoing to better quantify the potential for seroreversion, especially among the 1-dose group.

In addition to some women experiencing a decrease in antibodies over time, among the 1-dose group, approximately 6% and 8% of study participants had at least a 2-fold increase in antibody concentration against HPV-16 and HPV-18, respectively, during the study period. We hypothesize that increases in antibody levels may be due to an anamnestic response after natural exposure to HPV-16 or HPV-18 virions or those of closely related types. These antibody increases could contribute to additional protection as antibody levels decline, although this boosting effect would diminish as HPV infections become less prevalent in vaccinated populations.

In the early years after HPV vaccination, we and others consistently reported that antibody levels with 3 doses were approximately 4 times higher than levels with a single dose (11). Sixteen years after vaccination, we now highlight that because 3-dose antibody levels are declining at a faster absolute rate than single-dose levels are, the relative difference in the 1-dose and 3-dose antibody levels is decreasing. There is now a 3-fold difference between levels for HPV-16 and closer to a 2-fold difference for HPV-18. These findings reinforce the concept that the priming vaccination alone can efficiently generate long-lived plasma cells, implying that they can be generated directly from the activation of naive B cells, at least in the context of a particulate multivalent antigen such as the HPV virus-like particles. With additional booster doses, plasma blasts are also generated from memory B cells induced by the priming dose. These plasma cells, however, appear to have a shorter lifespan (12).

Strengths of our analysis include near-complete retention rates and active long-term follow-up over 16 years. In addition, antibodies against HPV-16 and HPV-18 were measured using a validated ELISA with excellent test characteristics (13). We emphasize that CVT participants were between 18 and 25 years of age when vaccinated and, at the 16-year follow-up visit, were between 33 and 42 years of age. The primary target population of immunization programs is adolescents aged 9 to 14 years, and antibody responses in girls are stronger than in women. Our results apply only to the bivalent HPV vaccine, to which antibody responses are stronger than to the quadrivalent vaccine (14). Our investigations in CVT continue to be post hoc and thus have a fixed sample size; a substantially large single-dose HPV vaccine group would have been needed for long-term virologic outcomes investigation. Our complementary ongoing Estudio de Comparacion de Una y Dos Dosis de Vacunas Contra el Virus de Papiloma Humano (ESCUDDO) clinical trial (15) will address whether the efficacy of a single-dose HPV vaccine is virologically noninferior to that of 2 doses in girls of the target age for routine vaccination.

Modeling exercises emphasize the importance of HPV vaccines protecting girls and women during the peak age periods of HPV acquisition (16). Based on our finding of nearly 100% seropositivity for HPV-16 and HPV-18 antibodies paired with modest declines in antibody response 16 years after a single HPV vaccination, we expect that women will have adequate protection throughout the critical years of HPV risk. Therefore, our study lends additional support to the World Health Organization recommendation of using a single-dose HPV vaccine schedule in immunization programs worldwide.

Data availability

A trial summary, current publications, and contact information for data access are available online at https://dceg.cancer.gov/research/who-we-study/cohorts/costa-rica-vaccine-trial.

Author contributions

Carolina Porras, MSc (Conceptualization; Investigation; Project administration; Writing—original draft; Funding acquisition); Byron Romero, MD (Investigation; Project administration; Writing—review & editing); Troy Kemp, PhD (Investigation; Validation; Writing—review & editing); Romain Fantin, MSc (Data curation; Formal analysis; Visualization; Writing—review & editing); Rolando Herrero, PhD (Conceptualization; Investigation; Supervision; Writing—original draft); Allan Hildesheim, PhD (Conceptualization; Writing—original draft); Rebeca Ocampo, MD (Writing—review & editing); Monica S. Sierra, PhD (Writing—review & editing); Mitchell H. Gail, MD, PhD (Formal analysis; Methodology; Conceptualization: Writing—review & editing); John Schussler, BSc (Data curation; Formal analysis; Visualization; Writing—review & editing; software); John T. Schiller, PhD (Conceptualization; Writing—original draft); Douglas R. Lowy, MD (Conceptualization; Writing—review & editing); Ligia A. Pinto, PhD (Investigation; Validation; Writing—review & editing); Danping Liu, PhD (Formal analysis; Methodology; Conceptualization: Writing—original draft; Visualization; Writing—review & editing; software); Aimée R. Kreimer, PhD (Conceptualization; Investigation; Supervision; Writing—original draft; Funding acquisition).

Funding

This work was supported by the National Cancer Institute (contract No. N01-CP-11005), with funding support from the National Institutes of Health Office of Research on Women’s Health. The CVT is a long-standing collaboration between investigators in Costa Rica and the National Cancer Institute. GlaxoSmithKline Biologicals provided vaccine and support for aspects of the trial associated with regulatory submission needs of the company under a Clinical Trials Agreement (US Food and Drug Administration BB-IND 7920) during the 4-year randomized, blinded phase of our study. The National Cancer Institute and Costa Rica investigators are responsible for the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation of the manuscript.

Monograph sponsorship

This article appears as part of the monograph “State of the Science of Single-Dose Prophylactic HPV Vaccination,” sponsored by the Bill & Melinda Gates Foundation.

Conflicts of interest

John T. Schiller and Douglas R. Lowy report that they are named inventors on US government–owned HPV vaccine patents, with expired licenses to GlaxoSmithKline and Merck. The other authors declare that they have no conflicts of interest.

Investigators in the CVT Group: Bernal Cortés, Paula González (deceased), Rolando Herrero, Silvia E. Jiménez, Carolina Porras, Ana Cecilia Rodríguez (Agencia Costarricense de Investigaciones Biomédicas, formerly Proyecto Epidemiológico Guanacaste, Fundación INCIENSA, San José, Costa Rica); Allan Hildesheim, Aimée R. Kreimer, Douglas R. Lowy, Mark Schiffman, John T. Schiller, Mark Sherman, Sholom Wacholder (deceased) (US National Cancer Institute, Bethesda, MD); Ligia A. Pinto, Troy J. Kemp (Leidos Biomedical Research, Inc, Frederick National Laboratory for Cancer Research, Frederick, MD); Mary K. Sidawy, (Georgetown University, Washington, DC); Wim Quint (deceased), Leen-Jan van Doorn, Linda Struijk (DDL Diagnostic Laboratory, the Netherlands); Joel M. Palefsky, Teresa M. Darragh (University of California, San Francisco, San Francisco, CA); and Mark H. Stoler (University of Virginia, Charlottesville, VA).

We dedicate this work to the memory of our beloved colleague and friend Paula Gonzalez, the principal investigator of the CVT long-term follow-up study. We extend a special thanks to the women of Guanacaste and Puntarenas, Costa Rica, who gave of themselves in participating in this effort. In Costa Rica, we acknowledge the tremendous effort and dedication of the staff involved in this project; we would like to specifically acknowledge the meaningful contributions of Carlos Avila, Loretto Carvajal, Rebeca Ocampo, Cristian Montero, and Diego Guillen. In the United States, we extend our appreciation to the team from Information Management Services responsible for the development and maintenance of the data system used in the trial and who serve as the data management center for this effort, especially Jean Cyr, Julie Buckland, John Schussler, and Brian Befano. We thank Dr Diane Solomon (CVT: medical monitor and quality control pathologist) for her invaluable contributions to the design and conduct of the trial and Nora Macklin and Kate Torres for their expertise in coordinating the study. We thank the members of the Data and Safety Monitoring Board charged with protecting the safety and interest of participants during the randomized, blinded phase of our study (Chair Steve Self , Adriana Benavides, Luis Diego Calzada, Ruth Karron, Ritu Nayar, and Nancy Roach) and members of the external Scientific HPV Working Group, who have contributed to the success of our efforts over the years (Henriette Raventós, Chair, Diane Davey, Gypsyamber D’Souza, Anne Gershon, Silvia Lara, Wasima Rida, Richard Roden, Maria del Rocío Sáenz Madrigal, and Margaret Stanley). We thank the Division of Cancer Epidemiology and Genetics Cancer Genomics Research Laboratory and acknowledge the support from Belynda Hicks, Casey Dagnall, and Amy Hutchinson.

Preliminary findings for this analysis were presented at the International Papillomavirus Conference in Washington DC, in April 2023.