First dose mRNA vaccination is sufficient to reactivate immunological memory to SARS-CoV-2 in ex COVID-19 subjects

Characterizing the adaptive immune response to COVID-19 vaccination in individuals who recovered from SARS-CoV-2 infection may define current and future clinical practice. To determine the effect of two doses BNT162b2 mRNA COVID-19 vaccination schedule in individuals who recovered from COVID-19 (ex COVID-19) compared to naive subjects we evaluated SARS-CoV-2 spike-specific T and B cell responses, as well as specific IgG, IgM and neutralizing antibodies titres in 22 individuals who received BNT162b2 mRNA COVID-19 vaccine, 11 of which had a previous history of SARS-CoV-2 infection. Evaluations were performed before vaccination and then weekly until 7 days post second injection. Data obtained clearly showed that one vaccine dose is sufficient to increase both cellular and humoral immune response in ex COVID-19 subjects without any additional improvement after the second dose. On the contrary, the second dose is mandatory in naive ones to further enhance the response. These results question whether a second vaccine jab in ex COVID-19 subjects is required and indicate that millions of vaccine doses may be redirected to naive individuals, thus shortening the time to reach herd immunity.