mRNA-based SARS-CoV-2 Comirnaty vaccine elicits weak and short specific memory B cell response in individuals with no previous infection.

Objectives: The dynamics of the memory B cell (MBC) repertoire after SARS-CoV-2 vaccination is crucial for assessing long-term immunity. We compare spike-specific MBC responses between SARS-CoV-2 unexposed and recovered individuals, and their impact on breakthrough infections during follow-up.

Methods: Spike-specific MBC and T cells were quantified at inclusion and after two doses of mRNA vaccine in a longitudinal cohort of 85 naïve and 64 recovered participants (47 with positive serology and 17 with negative serology after infection).

Risk of SARS-CoV-2 Reinfections in a Prospective Inception Cohort Study: Impact of COVID-19 Vaccination.

The risk of reinfection could be related to the initial SARS-CoV-2 clinical presentation, but there are no data about the risk change after SARS-CoV-2 vaccination. We evaluated the rate of reinfection in an inception cohort study of 4943 health care workers (HCWs) according to symptoms and serologic results during March−May 2020. Incidence rates (IR) and IR ratios (IRR) before and after SARS-CoV-2 vaccination were determined by adjusting Poisson models.