Serological responses to COVID-19 booster vaccine in England

IntroductionThere are limited data on immune responses after COVID-19 vaccine boosters in individuals receiving primary immunisation with BNT162b2 (Pfizer-BioNTech) or AZD1222 (AstraZeneca). MethodsA prospective, cohort study to assess SARS-CoV-2 antibody responses before and after booster vaccination with BNT162b2 in adults receiving either (i) two BNT162b2 doses <30 days apart (BNT162b2-control), (ii) two BNT162b2 doses [&ge;]30 days apart (BNT162b2-extended) or (iii) two AZD1222 doses [&ge;]30 days apart (AZD1222-extended) in London, England. SARS-CoV-2 spike protein antibody geometric mean titres (GMTs) before and 2-4 weeks after booster were compared. ResultsOf 750 participants, 626 provided serum samples for up to 38 weeks after their second vaccine dose. Antibody GMTs peaked at 2-4 weeks after the second dose, before declining by 68% at 36-38 weeks after dose 2 for BNT162b2-control participants, 85% at 24-29 weeks for BNT162b2-extended participants and 78% at 24-29 weeks for AZD1222-extended participants. Antibody GMTs was highest in BNT162b2-extended participants (942 [95%CI, 797-1113]) than AZD1222-extended (183 [124-268]) participants at 24-29 weeks or BNT162b2-control participants at 36-38 weeks (208; 95%CI, 150-289). At 2-4 weeks after booster, GMTs were significantly higher than after primary vaccination in all three groups: 18,104 (95%CI, 13,911-23,560; n=47) in BNT162b2-control (76.3-fold), 13,980 (11,902-16,421; n=118) in BNT162b2-extended (15.9-fold) and 10,799 (8,510-13,704; n=43) in AZD1222-extended (57.2-fold) participants. BNT162b2-control participants (median:262 days) had a longer interval between primary and booster doses than BNT162b2-extended or AZD1222-extended (both median:186 days) participants. ConclusionsWe observed rapid serological responses to boosting with BNT162b2, irrespective of vaccine type or schedule used for primary immunisation, with higher post-booster responses with longer interval between primary immunisation and boosting. Boosters will not only provide additional protection for those at highest risk of severe COVID-19 but also prevent infection and, therefore, interrupt transmission, thereby reducing infections rates in the population. Ongoing surveillance will be important for monitoring the duration of protection after the booster.