Differential vaccine-induced kinetics of humoral and cellular immune responses in SARS-CoV-2 naive and convalescent health care workers

Abstract

Effective vaccination is a key element in the exit strategy from the current severe acute respiratory syndrome- CoV coronavirus-2 (SARS-CoV-2) pandemic, and may also offer protection against severe disease from future variants of concern. Here we prospectively monitored T- cell responses over time, using ELISpot interferon-γ (INF-y) release assays, and B- cell responses, using serological tests, after vaccination and booster with BioNTech/Pfizer mRNA (Pfizer) and Janssen vector (Janssen/Johnson & Johnson) vaccines in hospital health care workers. Vaccine recipients were divided into seropositive and seronegative individuals at baseline, in order to determine the effect of natural immunity on vaccine-induced immune kinetics.

We found that convalescent individuals mounted higher spike-specific INF-y-secreting T cell responses and B- cell-mediated IgG responses, after receiving the Janssen vaccine or the first dose of the Pfizer vaccine. IgG levels corresponded to the virus neutralisation capacity as measured by VNT assay. At 8 months post vaccination, spike-specific cellular immunity waned to low levels in individuals with or without prior natural immunity, whereas waning of humoral immunity occurred predominantly in naive individuals. The booster shot effectively re-induced both cellular and humoral immune responses.

To conclude, our data supports the implemented single-dose mRNA booster strategy employed in the Netherlands. Furthermore, the level of pre-existing natural immunity may be factored into determining the optimal time window between future booster vaccines.