Enhanced immune responses to mRNA compared with adenoviral vector COVID-19 vaccines during pregnancy: implications for pandemic preparedness.

INTRODUCTION

Multiple SARS-CoV-2 vaccine types are available but the optimal platform for use in pregnancy remains unclear. This study compared humoral and cellular immune responses in blood and breastmilk following COVID-19 vaccination with different vaccine types during pregnancy.

METHODS

In a prospective cohort study, pregnant individuals (85 % naïve for COVID-19) received at least one dose of either the adenoviral vector vaccine (AVV) ChadOx1-S (N = 17) or a messenger RNA vaccine (mRNAV) BNT162b2 (N = 42) or mRNA-1273 (N = 5) during pregnancy. Blood samples were taken at different timepoints before and after each vaccine dose, and at delivery. Breastmilk samples were collected up to 12 weeks postpartum. Follow-up continued until 28-35 days after postpartum mRNA booster vaccination (BNT162b2: N = 23; mRNA-1273: N = 25). The primary outcome was comparison of immune responses between the AVV and mRNAV group.

RESULTS

mRNAV recipients showed significantly higher anti-RBD IgG titres, with greater avidity and neutralizing capacity, and stronger S1- and S2-specific CD154 CD4+ T-cell responses up to day 28 after the second vaccine dose. Cord blood from mRNAV recipients had significantly higher anti-RBD IgG and NAb titres at delivery compared to AV vaccinated individuals. After postpartum mRNA booster vaccination, immune responses were comparable between both groups.

CONCLUSION

mRNA COVID-19 vaccination during pregnancy elicited more rapid and robust immune responses compared to AV vaccination. These findings suggest that mRNA vaccines may be preferable for emergency use during pregnancy and support their use in future maternal vaccine development and in pandemic preparedness recommendations.

CLINICAL TRIAL REGISTRY: Clinicaltrials.govidentifier: NCT05618548.