People with a previous SARS-CoV-2 infection had a large number of spike-specific memory B cells before vaccination, and after the first dose of an mRNA vaccine, had a significant boost in spike-specific memory B cells — but not after the second dose;
Despite the weaker response to the second mRNA dose, people with a previous SARS-CoV-2 infection still ended up with a larger number of spike-specific memory B cells than fully vaccinated people who never had the virus, and;
The spike-specific memory B cells in people with a previous SARS-CoV-2 infection bound more tightly to the spike protein of the virus compared to the memory B cells induced in uninfected people after a single mRNA vaccination.