Determinants of SARS-CoV-2 anti-spike antibody levels following BNT162b2 vaccination: cross-sectional analysis of 6,000 SIREN study participants

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Abstract Background Understanding immunological responses to SARS-CoV-2 vaccinations is integral to the management of SARS-CoV-2. We aimed to investigate determinants of antibody response to the BNT162b2 vaccine. Methods A cross-sectional analysis of anti-spike binding antibodies in serum samples from healthcare workers after one or two doses. Post-vaccination interval was restricted to ≥21 days after dose 1, ≥14 days after dose 2. The primary outcome was anti-S titres with explanatory variables dose, previous infection, dosing interval, age, ethnicity, and comorbidities. Multivariable linear regression was also conducted. Results Participants (n=5,871) included 3,989 post-dose 1, 1,882 post-dose 2. In SARS-CoV-2 infection naïve, 99.65% seroconverted after dose 1 and >99.9% seroconverted after dose 2. Geometric mean anti-S titre in the naïve cohort was 75.48 Binding Antibody Units/ml after dose 1, 7,049 BAU/ml after dose 2. Anti-S titres were higher in those with previous infection (2,111 BAU/ml post-dose 1, 16,052 BAU/ml post-dose 2), and increased with time between infection and vaccination: 3 months 1,970 (1,506-2,579) vs 9 months; 13,759 (8,097-23,379). Longer dosing intervals increased antibody response post-dose 2: 11-fold higher with a longer interval (>10 weeks) than those with shorter intervals, across all age-groups. Younger participants had higher mean titres (>2.2-fold higher). Multivariable regression modelling corroborated the above associations, and also found higher titres associated with being female or from an ethnic minority but lower titres among immunocompromised participants. Conclusion The number of antigen exposures and timing between vaccinations plays a significant role in the magnitude of the post-vaccination antibody response, with implications for long-term protection and post-booster antibody responses.

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