One dose of SARS-CoV-2 vaccine exponentially increases antibodies in recovered individuals with symptomatic COVID-19.

Levi, Riccardo; Azzolini, Elena; Pozzi, Chiara; Ubaldi, Leonardo; Lagioia, Michele; Mantovani, Alberto; Rescigno, Maria

BACKGROUND Currently used COVID-19 vaccines require two doses to achieve optimal vaccination, and there is no indication as to whether individuals who have been exposed to SARS-CoV-2 should be vaccinated, or should receive one or two vaccine doses. METHODS Here, we tested the antibody response developed after administration of the Pfizer/BioNTech vaccine in 124 healthcare professionals of which 57 had a previous history of SARS-CoV-2 exposure (SARS-CoV-2-Exp), with or without symptoms. RESULTS Post-vaccine antibodies in SARS-CoV-2 exposed individuals increased exponentially within 5-18 days after the first dose compared to naïve subjects (P < 0.0001). In a multivariate Linear Regression (LR) model we showed that the antibody response depended on the IgG pre-vaccine titer and on the exposure to SARS-CoV-2. In symptomatic SARS-CoV-2 exposed individuals, IgG reached a plateau after the second dose, and those that voluntarily refrained from receiving the second dose (n = 7) retained their antibody response. Gastrointestinal symptoms, muscle pain and fever significantly positively correlated with increased IgG responses. By contrast, all a/paucisymptomatic and unexposed individuals showed an important increase after the second dose. CONCLUSION Thus, one vaccine dose is sufficient in symptomatic SARS-CoV-2 exposed subjects to reach a high titer of antibodies suggesting no need for a second dose, particularly in light of current vaccine shortage. TRIAL REGISTRATION ClincalTrials.gov NCT04387929FUNDING. This work was partially supported by a philantropic donation by Dolce & Gabbana and by the Italian Ministry of Health (Ricerca corrente).