Population homogeneity for the antibody response to COVID-19 Comirnaty vaccine is only reached after the second dose

While mRNA vaccines authorized for emergency use are administrated worldwide in an effort to contain the COVID19 crisis, little is known about the heterogeneity of the immune response they induce. Here, we report the first 6 weeks of a longitudinal study that quantifies the humoral immune response to BNT162b2 mRNA COVID-19 (Pfizer/BioNTech, Comirnaty) in 1245 health care providers, the Lx1000HCW-PZF cohort. We reveal a striking inter-individual variation 3 weeks after the 1st dose administration that only in part related to age and sex. While population homogeneity in robust IgG responses was reached upon 2nd dose administration, IgM and IgA levels remain low and heterogenous. Our findings of isotypic and heterogenous antibody responses to Comirnaty highlight the need for evaluating the efficacy of COVID-19 mRNA vaccine in preventing infection aside disease, and - contrary to what has been proposed - advocate for the interval between the two doses not to be extended.