Immunogenicity of tetanus, diphtheria and acellular pertussis vaccination among pregnant women living with and without HIV

Abstract

Objective:

Vaccination during pregnancy with tetanus–diphtheria–acellular pertussis (Tdap) vaccine is recommended to protect the young infants against pertussis. There is a paucity of data on immune responses to Tdap in pregnant women with HIV (PWWH), and its impact on the protection of their infants has not been described.

Methods:

In an open label phase IV clinical trial in South Africa, we evaluated the immunogenicity and safety of Tdap in PWWH compared with HIV-uninfected women. Antigen-specific immunoglobulin G (IgG) to pertussis toxoid, filamentous haemagglutinin, pertactin, fimbriae, diphtheria and tetanus were measured by electrochemiluminescence-based multiplex assay.

Results:

Overall, 91 PWWH and 136 HIV-uninfected pregnant women were enrolled. All PWWH were on antiretroviral treatment and 94.5% had HIV viral loads <40 copies per millilitre. Antibody levels prevaccination were lower among PWWH compared with HIV-uninfected women for all antigens. At 1 month postvaccination PWWH compared with HIV-uninfected women had lower fold-increase and antibody concentrations for all epitopes. Also, a lower proportion of PWWH achieved ≥4-fold increase from pre to postvaccination for pertussis toxoid and pertactin, or diphtheria IgG levels ≥0.1 IU/ml and ≥1 IU/ml postvaccination. Adverse events postvaccination were similar in PWWH and HIV-uninfected.

Conclusion:

Tdap vaccination was safe and immunogenic. PWHW had, however, attenuated humoral immune responses, which could affect the effectiveness of protecting their infants against pertussis compared with those born to women without HIV.

ClinicalTrials.gov identifier: NCT05264662

Introduction

Pertussis (whooping cough) is a highly contagious vaccine-preventable respiratory tract disease, caused by the bacterium Bordetella pertussis. Pertussis can affect people of all ages; however, young unimmunised or partially immunised infants are the most vulnerable group for severe illness and death [1]. In 2014, there were an estimated 24.1 million pertussis cases and 160 700 associated deaths worldwide, with the African region having the largest burden (7.8 million cases and 92 500 deaths). Globally, infants (<12 months of age) account for 5.1 million cases and approximately 85,900 deaths annually [1].

To reduce the susceptibility window period for pertussis between birth and the third dose of the primary vaccination series in infancy, acellular pertussis (aP)-containing vaccines are recommended during pregnancy. Following the initial recommendations in 2011–2012 from the UK and the USA, many other countries have implemented routine vaccination with aP-containing vaccine during pregnancy [2]. Nevertheless, use of aP-containing vaccines during pregnancy has not as yet been adopted into public immunization programs of any African country. Studies from countries with low prevalence of human immunodeficiency virus (HIV) infection in pregnant women report that aP vaccination induces good immune responses during pregnancy and the active transplacental transfer of pertussis immunoglobulin G (IgG) to the foetus. Furthermore, vaccination with aP-containing vaccines is safe to the women, with no adverse pregnancy outcomes of concern [3]. Vaccine effectiveness estimates of maternal vaccination against severe pertussis in their young infants (<3 months of age) is 91% to 94% for pertussis-associated hospitalization and 95% for pertussis-related deaths [4].

Pregnant women, and adults in general, living with HIV have lower humoral immune responses to vaccination, compared with their HIV-uninfected counterparts [5,6,7] Consequently, it is necessary to investigate the immune responses of aP-containing vaccines in pregnant women with HIV (PWWH), to understand the relative protection of their infants against pertussis compared with offspring born to women without HIV. This is pertinent in many sub-Saharan African countries where there remains a high prevalence of HIV in women of childbearing age. South Africa has an estimated 8.4 million people living with HIV and in 2019 the national antenatal HIV prevalence was estimated at 30% [8].

We undertook an open label phase IV clinical trial to evaluate the immunogenicity and safety of an adult formulation of tetanus–diphtheria–acellular pertussis (Tdap) vaccine in PWWH compared with HIV-uninfected women.

Methods

Pregnant women attending antenatal care at clinics in Soweto, South Africa, were screened for enrolment into the study. Healthy, pregnant women 18–39 years of age, 20–36 weeks of gestational age of a singleton pregnancy, considered to be at low risk for complications, and documented to be HIV-infected or HIV-uninfected were eligible for enrolment (full inclusion and exclusion criteria in supplement). In South Africa, pregnant women attending public antenatal clinics are offered tetanus-toxoid containing vaccines and seasonal influenza vaccines, but not Tdap [9]. After written informed consent was obtained, and detailed demographic, obstetric and medical information was collected, women received commercially available Adacel (Sanofi, France) vaccine.

Venous blood was collected just prior to vaccination and at 28–35 days postvaccination. Solicited injection-site and systemic adverse events (AEs) were recorded on a diary card for seven days postvaccination. Unsolicited AEs and serious AEs (SAEs) were collected for the duration of the study. Serum was tested by electrochemiluminescence-based multiplex assay (using technology from Meso Scale Diagnostics) for IgG against pertussis-toxoid (PT), filamentous haemagglutinin (FHA), pertactin (PRN), fimbriae (FIM) (reported as ELISA units [EU]/ml), diphtheria and tetanus (reported as international units [IU]/ml). The method was developed and validated at Sanofi and has been described in detail [10]. All assays were performed in the laboratories of Sanofi in Swiftwater, Pennsylvania, USA, in a blinded manner to the HIV status of the participant.

The study was designed with two co-primary objectives: describe antibody responses to all Tdap epitopes in PWWH compared with HIV-uninfected pregnant women before and 1 month after Adacel vaccination; describe IgG responses to all Tdap and Hexavalent antigens in infants born to mothers who received Adacel and those born to mothers not vaccinated, stratified by maternal HIV status. A sample size of 90 vaccinated PWWH and their infants, 90 infants born to unvaccinated PWWH, 135 HIV-uninfected vaccinated women and their infants, and 135 infants born to HIV-uninfected unvaccinated women would provide 80% power to detect the difference in IgG levels both in the women and the infants (details in supplement). The current analysis describes the immunogenicity results of Tdap in the women, and safety analyses including outcomes reported from vaccination to postvaccination visit.

Participants’ characteristics were compared between PWWH and HIV-uninfected women. Geometric mean antibody concentrations (GMCs) and the corresponding 95% confidence interval (CI) were estimated using logarithmic transformation, the percentage of participants achieving ≥4-fold increase in PT, FHA, PRN and FIM IgG levels from pre to postvaccination, besides the percentage of those with tetanus and diphtheria IgG ≥0.1 IU/ml and ≥1 IU/ml was calculated, and compared between PWWH and HIV-uninfected women by univariate and multivariate regression analyses. Postvaccination immunogenicity analyses including only women in whom the postvaccination visits were done within a 28–35 days window period were performed. Reporting on AEs and SAEs were descriptive.

The study was approved by the University of the Witwatersrand Human Research Ethics Committee (210706). ClinicalTrials.gov identifier: NCT05264662.

Results

From 7 March to 12 September 2022, 227 pregnant women were enrolled and provided prevaccination serum, including 91 PWWH and 136 HIV-uninfected (study consort diagram in supplement, Figure S1). The participants’ characteristics were similar between the two study groups, except for PWWH being older (30.7 years) and less likely to be primigravida (5.5%) compared with HIV-uninfected women (27.3 years and 27.9%, P < 0.001 for both comparisons), Table 1. All PWWH were on antiretroviral treatment (ART), the median CD4+ T-lymphocyte count was 561.5cells/μL and 94.5% had HIV viral loads < 40 copies/ml at the time of vaccination. Overall, 220 women had a postvaccination visit, including 210 (95.5%) within 28–35 days postvaccination.

Table 1.

Characteristics at enrolment for all vaccinated women by HIV status.

	Overall N = 227	HIV-N = 136	PWWH N = 91	P-value
Number of Black African race (%)	227 (100)	136 (100)	91 (100)	n.a.
Mean age (standard deviation); years	28.7 (5.5)	27.3 (5.5)	30.7 (4.9)	<0.001
Mean MUAC (standard deviation); cm	29.4 (3.9) [195]	29.4 (3.9) [112]	29.3 (4.0) [83]	0.88
Mean BMI (standard deviation)	30.8 (6.1) [194]	30.8 (5.7) [111]	30.7 (6.5) [83]	0.98
Mean gestational age (standard deviation); weeks	28.7 (4.1)	28.9 (3.9)	28.2 (4.4)	0.29
Number of primigravida (%)	43 (18.9)	38 (27.7)	5 (5.5)	<0.001
Median gravidity (IQR)	2 (1.5, 2.5)	2 (1, 3)	3 (2.5, 3.5)	<0.001
Number smoking during pregnancy (%)	10 (4.4)	4 (2.9)	6 (6.6)	0.20
Number drinking alcohol during pregnancy (%)	7 (3.1)	3 (2.2)	4 (4.4)	0.44
Number with less than 12 years of education (%)	65 (28.6)	32 (23.4)	33 (36.3)	0.11
Number with 12 years of education (%)	135 (59.5)	86 (62.8)	49 (53.9)
Number with tertiary education (%)	28 (12.3)	19 (13.9)	9 (9.9)
Number vaccinated with at least one TT dose during this pregnancy (%)	117 (51.5)	65 (47.8)	52 (57.1)	0.17
Median TT doses during this pregnancy (IQR)	1 (0, 1)	0 (0, 1)	1 (0, 1)	0.09
Number on antiretroviral treatment (%)a	n.a.	n.a.	91 (100)	n.a.
HIV-1 viral load at enrolment <40 copies per milliliter (%)	n.a.	n.a.	86 (94.5)	n.a.
Median CD4+ T-lymphocyte count (IQR); cells per microliter	n.a.	n.a.	561.5 (383, 788)	n.a.
Mean days between vaccination and postvaccination visit (Standard deviation)	28.9 (2.8) [220]	29.0 (2.7) [132]	28.7 (3.0) [88]	0.45
Number of postvaccination visits within window period (%)b	210 (95.5) [220]	125 (94.7) [132]	85 (96.6) [88]	0.74
Number of deliveries before postvaccination visit	9	5	4	n.a.

BMI, body mass index; HIV, HIV-uninfected pregnant women; IQR, interquartile range; MUAC, mid-upper arm circumference; n.a., nonapplicable; PWWH, pregnant women with HIV; TT, tetanus toxoid containing vaccine.

Number in brackets represent the number of participants with available information if different from N and information in parentheses was calculated taking this in consideration.

^a89 were on first line therapy (19 on Tenofovir, Emtricitabine, Efavirenz fixed dose combination, and 70 on Tenofovir, Lamivudine, Dolutegravir [TLD] fixed dose combination), 1 was on second line therapy (Lamivudine/Zidovudine/Atazanavir/Ritonavir) and 1 on third line therapy (Darunavir/Ritonavir/TLD).

^bPer-protocol visits window period, 28–35 days between visits.

Prevaccination pertussis specific epitope IgG levels were lower among PWWH compared with HIV-uninfected women for all four pertussis antigens, Table 2. Despite increase in IgG levels in both groups 1 month postvaccination, PWWH had significantly lower fold-rise and antibody levels compared with HIV-uninfected women. The proportion of women achieving ≥4-fold increase in IgG from pre to postvaccination was also lower in PWWH compared with women without HIV for PT and PRN, Table 2. PWWH achieving ≥4-fold increase in PRN IgG had higher median CD4⁺ T-lymphocyte count (585.5cells/μl IQR: 434, 808.5) compared with those not reaching that threshold (373.5 cells/μl IQR: 277, 633; P = 0.034), although no such effect was observed for the other antigens.

Table 2.

Immune responses among pregnant women living with and without HIV to pertussis antigens.

	PERTUSSIS PT			Pertussis FHA			Pertussis FIM			Pertussis PRN
	HIV−	PWWH	P-value/aP-value	HIV−	PWWH	P-value/aP-value	HIV−	PWWH	P-value/aP-value	HIV−	PWWH	P-value/aP-value
GMCs prevaccination (95% CI)	10.3 (8.6, 12.4) [134]	7.2 (5.9, 9.0) [89]	0.015/0.033	26.9 (23.5, 30.7) [136]	18.9 (15.1, 23.6) [91]	0.005/0.010	10.9 (8.6, 13.7) [136]	4.6 (3.4, 6.2) [91]	<0.001/0.021	4.9 (3.9, 6.1) [136]	3.2 (2.5, 4.1) [91]	0.012/0.027
GMCs postvaccination (95% CI)	98.7 (87.0, 111.9) [132]	50.8 (41.1, 62.6) [88]	<0.001/<0.001	488.3 (423.9, 562.4) [132]	241.2 (190.7, 305.0) [88]	<0.001/<0.001	799.5 (597.1, 1070.6) [132]	214.7 (146.1, 315.5) [88]	<0.001/<0.001	170.8 (134.3, 217.2) [132]	66.0 (45.1, 96.5) [88]	<0.001/<0.001
GMCs at 28–35 days postvaccination (95% CI)a	101.7 (89.4, 115.6) [125]	50.9 (41.1, 63.1) [85]	<0.001/<0.001	483.0 (419.1, 556.6) [125]	236.8 (185.9, 301.7) [85]	<0.001/<0.001	822.2 (608.6, 1110.8) [125]	231.6 (158.8, 337.9) [85]	<0.001/0.001	178.4 (140.1, 227.3) [125]	66.6 (45.7, 96.9) [85]	<0.001/<0.001
Geometric mean fold rise; (95% CI)	9.8 (8.4, 11.5) [130]	7.1 (5.8, 8.6) [86]	0.010/0.011	18.1 (15.2, 21.5) [132]	12.7 (10.0,16.2) [88]	0.019/0.006	74.8 (59.4, 94.4) [132]	47.2 (34.9, 63.9) [88]	0.016/0.037	34.6 (28.0, 42.8) [132]	20.4 (14.6, 28.6) [88]	0.006/0.005
Geometric mean fold rise; (95% CI)a	9.8 (8.3, 11.5) [124]	7.1 (5.8, 8.7) [83]	0.017/0.017	17.7 (14.8, 21.2) [125]	12.3 (9.6, 15.8) [85]	0.018/0.008	74.3 (58.3, 94.7) [125]	49.9 (37.1, 67.2) [85]	0.040/0.073	34.6 (27.8, 43.2) [125]	21.0 (15.0, 29.4) [85]	0.011/0.011
≥4-fold increase from pre to postvaccination; n (%)	117 (90.0) [130]	65 (75.6) [86]	0.004/0.003	122 (92.4) [132]	77 (87.5) [88]	0.23/0.11	130 (98.5) [132]	83 (94.3) [88]	0.11/0.15	129 (97.7) [132]	76 (86.4) [88]	0.004/0.012
≥4-fold increase from pre to postvaccination; n (%)a	111 (89.5) [124]	62 (74.7) [83]	0.006/0.003	115 (92.0) [125]	74 (86.9) [85]	0.25/0.13	123 (98.4) [125]	81 (95.3) [85]	0.21/0.26	122 (97.6) [125]	74 (87.1) [85]	0.007/0.021

95% CI, 95% confidence interval; FHA, filamentous haemagglutinin; FIM, fimbriae; GMCs, geometric means concentrations; HIV, HIV-uninfected pregnant women; PRN, pertactin; PT, pertussis toxoid; PWWH, pregnant women with HIV.

aP-value: P-value adjusted for age and primigravida (yes/no).

Number in brackets represent the number of participants with available information and information in parentheses was calculated taking this in consideration.

^aOnly women who attended the visits within the protocol defined window period were included.

For diphtheria and tetanus, PWWH had lower pre and postvaccination antibody levels. With >85% of all women having already prevaccination antibody levels for tetanus ≥1 IU/ml. While all women achieved IgG levels ≥0.1 IU/ml and ≥1 IU/ml postvaccination for tetanus, a lower proportion of PWWH than HIV-uninfected women achieved those thresholds for diphtheria, Table S1 in supplement.

During the first week postvaccination, the most commonly reported local injection site reaction was itching by both PWWH (51.1%) and HIV-uninfected women (43.2%); weakness/tiredness was the most frequent systemic reaction reported by those living with (37.8%) and without (33.3%) HIV, Table S2 in supplement. There were no differences in the frequency of solicited AEs between the two study groups. Overall, 34 SAEs were reported, including seven episodes of gestational hypertension and four premature labour events, Table S3 in supplement. However, of all the SAEs only one premature labour that occurred two days after vaccination of a HIV-uninfected woman was considered as being possibly related to vaccination based solely on temporal association. AEs reported from vaccination to 1 month postvaccination are shown in Table S4 in supplement.

Discussion

In this trial, PWWH on ART and with well controlled HIV infection had lower antibody levels for all assessed antigens compared with HIV-uninfected pregnant women at enrolment. Tdap elicited an antibody response in both study groups, although PWWH continued to display lower antibody levels and lower fold-rise postvaccination. As no correlate of protection is available for pertussis, the surrogate for measuring immune response was defined as ≥4-fold increase in antibody levels from pre to postvaccination [11]; using this criterion >75% of PWWH seroconverted to PT. Despite a less robust immune response among PWWH, vaccination might still confer some protection to in-utero HIV exposed young infants, through transplacentally transferred antibodies. Our group had previously shown that HIV exposed infants (born to unvaccinated mothers) had similar PT and FHA antibody levels compared with HIV-unexposed infants prior to their first dose of pertussis-containing vaccine at seven weeks of age, suggesting that unvaccinated mothers had similar transplacental antibody transfer independently of maternal HIV infection status [11].

A systematic review and meta-analysis of data from 37 low- and middle-income countries, described that the case fatality rate among confirmed pertussis cases was 7.2% during the first year of life in the studies reporting deaths, and that HIV exposure was associated with higher pertussis incidence, higher rates of hospitalisation and pertussis-related deaths (although data were limited by the number of countries reporting HIV status) [12]. Due to the higher burden of pertussis in infants born to mothers living with HIV, vaccinating PWWH even if with lower immune response may impact disease burden. We will evaluate the antibody concentration in the infants born to the mothers in our study and comparing those to infants born to unvaccinated mothers will allow us to better predict protection against infant disease. A recent hospital-based pneumonia surveillance study in South Africa identified adults living with HIV as an important group at risk of severe pertussis, and alerted to the need for more regular booster vaccination in this population, including pregnant women [13].

Some studies reported that low HIV viral loads, and high CD4⁺ T-lymphocyte counts, correlated with improved immune responses to influenza vaccines in adults living with HIV [14,15]. In our study, only for PRN IgG PWWH achieving ≥4-fold increase had higher median CD4⁺ T-lymphocyte counts than those not achieving. Additionally, no effect on immune response was observed according to viral load (data not shown); however, 94.5% of the PWWH had undetectable viral load.

A limitation of our study was the noninclusion of a placebo control group, although since the primary objective of the current analysis was to compare immune responses of PWWH to those of HIV-uninfected, the control group would be more relevant for a complete safety assessment. Our study, however, supports the tolerability of Tdap during pregnancy and no increased reactogenicity was detected in PWWH. Randomized controlled trials and large observational studies have not identified any SAEs or adverse pregnancy outcomes associated with Tdap during pregnancy [4]. Also, we did not collect information on prior pertussis vaccination. A combined infant whole-cell pertussis vaccine was introduced in South Africa in 1957 and in 2009 the country changed from whole-cell pertussis vaccines to acellular pertussis-containing vaccine given at 6, 10, and 14 weeks of age followed by a booster at 18 months of age. Since adolescent and adult boosters are not routinely offered in South Africa we expect that both study groups would have similar vaccination histories.

Vaccination of PWWH may benefit from different approaches, such as more immunogenic vaccines, high dose vaccines or more than one dose possibly with different schedules, to increase the level of antibodies transfer to the foetus and confer protection to the HIV exposed infant. We will be reporting on the infants’ follow-up regarding antibody levels pre and postprimary vaccination series and booster vaccination.

Acknowledgements

The authors would like to thank all the study participants, and the Wits-Vida staff.

Funding: This study was supported by a grant from Sanofi (TD500058).

Conflicts of interest

M.C.N. reports grants from the Bill & Melinda Gates Foundation, European & Developing Countries Clinical Trials Partnership, Pfizer, AstraZeneca, and Sanofi; and personal fees from Pfizer and Sanofi. S.A.M. reports grants and personal fees from the Bill & Melinda Gates Foundation, and grants from the South African Medical Research Council, Novavax, Pfizer, Minervax, and European & Developing Countries Clinical Trials Partnership. The other authors report no conflicts of interest.