The effect of pertussis vaccination in pregnancy on the immunogenicity of acellular or whole-cell pertussis vaccination in Gambian infants (GaPS): a single-centre, randomised, controlled, double-blind, phase 4 trial

Abstract

<p><b>Background</b><br></p><p>Vaccinating women against pertussis in pregnancy protects young infants from severe disease and death. Vaccination-induced maternally derived antibodies, however, might subsequently modulate (and specifically blunt) the infant's serological response to their primary series of pertussis vaccinations. We examined the effect of pertussis immunisation in pregnancy on the immunogenicity of primary acellular or whole-cell pertussis vaccines in a west African cohort.<br></p><p><b>Methods</b><br></p><p>GaPs was a randomised, controlled, double-blind, phase 4 trial conducted in The Gambia. We used a predefined block randomisation scheme to randomly assign healthy, HIV-negative, pregnant participants (1:1) to receive a pertussis-containing (tetanus-diphtheria-acellular pertussis-inactivated polio virus [Tdap-IPV]) or tetanus-toxoid only vaccine at 28–34 weeks' gestation. At the same time, their infants were randomly assigned (1:1) to receive diphtheria-tetanus-acellular pertussis (DTaP) or diphtheria-tetanus-whole-cell pertussis (DTwP) primary vaccine at 8, 12, and 16 weeks postnatally. Participants and trial staff were masked to the allocation of the maternal vaccine. The field team and participants became unmasked to the allocation of the infant vaccine at 16 weeks; laboratory staff and all other investigators remained masked to infant vaccine allocation until the end of the trial. The primary outcome was geometric mean concentration (GMC) of infant pertussis toxin-specific antibodies at 20 weeks and 9 months postnatally and was assessed in infants who received all three doses of the primary vaccine. Secondary outcomes included memory B-cell responses, and exploratory outcomes were total pertussis-specific antibody binding concentrations and functional antibody titres (pertussis toxin-specific neutralising activity [PTNA] and serum bactericidal activity [SBA]). Vaccine reactogenicity was assessed in mothers and infants for 3 days after each vaccine dose. Pregnant women had an extra safety visit 7 days after vaccination. The study is registered with ClinicalTrials.gov, NCT03606096.</p><p><b>Findings</b><br></p><p>Between Feb 13, 2019, and May 17, 2021, we enrolled 343 maternal–infant pairs. 239 (77%) infants were included in the per-protocol immunogenicity analysis. Among infants of mothers receiving Tdap-IPV in pregnancy, at 20 weeks postnatally, the GMCs of anti-pertussis toxin IgG were more than three-fold lower in infants vaccinated with three doses of DTwP (n=64) than in infants vaccinated with three doses of DTaP (n=53; adjusted geometric mean ratio 0·28, 98·75% CI 0·16–0·50). This difference persisted up to 9 months (0·31, 0·17–0·55). Conversely, among infants born to tetanus toxoid-immunised mothers, post-vaccination GMCs of anti-pertussis toxin IgG at 9 months were higher in those vaccinated with DTwP (n=58) than in those vaccinated with DTaP (n=64; 2·02, 1·15–3·55). Tdap-IPV immunisation in pregnancy blunted anti-pertussis toxin IgG following primary vaccination in all infants but particularly in those receiving DTwP, with GMCs of anti-pertussis toxin IgG more than eight-fold lower in DTwP-vaccinated infants born to Tdap-IPV-vaccinated mothers than in DTwP-vaccinated infants born to tetanus toxoid-immunised mothers (0·12, 98·75% CI 0·07–0·22 at 20 weeks; 0·07, 0·03–0·17 at 9 months). Similarly, DTwP-vaccinated infants born to Tdap-IPV-vaccinated mothers also showed significant blunting of PTNA, SBA, total pertussis-specific antibody binding, and memory B-cell responses after primary immunisation, whereas minimal blunting was observed among DTaP-vaccinated infants. However, the absolute levels of these responses generated by DTwP-vaccinated infants remained similar to or, in many cases, were higher than those generated by DTaP-vaccinated infants. There was no difference in reactogenicity between the two maternal vaccines, with most reactions graded 0 or 1. There were no serious adverse events related to vaccination or trial participation.</p><p><b>Interpretation</b><br></p><p>Vaccinating women with Tdap-IPV in pregnancy was safe and well tolerated in a sub-Saharan African setting and boosted the quantity and quality of pertussis-specific antibodies in infants in early life. Although Tdap-IPV was associated with relative blunting of the immune response to the DTwP primary vaccination series, pertussis-specific antibody quality and memory B-cell responses were nevertheless preserved, regardless of the vaccine given during pregnancy.</p>