Timing and implications for immune response to vaccine in SARS-CoV-2 breakthrough infections

COVID-19 vaccines elicit a strong anti-S antibodies response. We aim to describe antibody titers in peri-vaccination SARS-CoV-2 infections. This is a retrospective longitudinal single-cohort study. Serological tests were performed at the time of the first SARS-CoV-2 vaccine dose (T0) and 60 (T1), 120 (T2), and 240 (T3) days after. The study included 4,682 subjects. Group A had the infection without an anti-S Ig response. Group B and C seroconverted for anti-N Ig between T0 and T1 and be-tween T1 and T2, respectively. Group D was persistently anti-N Ig negative. Group B showed an initial sub-optimal response, reaching the highest titer at T3. Those who received the second dose 120 days after the infection had higher titers compared to those who received it 21 days after the first dose. The immune response depends on the number and the timing of vaccine doses, highlighting the need for a more personalized approach to vaccination.