Immunological memory and neutralizing activity to a single dose of COVID-19 vaccine in previously infected individuals

Background: The efficacy of COVID-19 vaccines to generate immunological memory post-vaccination has not previously been studied. Objective: To assess immunological memory in previously SARS-CoV-2 infected individuals after a single dose of mRNA vaccine. Patients and methods: Healthcare workers (n = 280) were enrolled after obtaining written informed consent and grouped under previously infected and no prior exposure (reverse transcription-polymerase chain reaction positive and negative, respectively). Blood was drawn at baseline and post-vaccination (single dose of COVISHIELD) for enumerating neutralizing antibodies by chemiluminescence and memory T- and B-cells by flow cytometry. Results: Post vaccination, compared with the no prior exposure group, the previously infected group had higher levels of: antibody response (1124.73 +/- 869.13 vs 94.23 +/- 140.06 AU/ml, p = 0.0001); CD4 memory T-cells: central memory CCR7+CD45RA- (p = 0.0001), effector memory CCR7-/CD45RA- (p = 0.01); total CD8+ T-cells (p = 0.004); CD8+ naive T-cells CCR7+CD45RA+ (p = 0.01); and memory B-cells CD20+CD27+ (p = 0.0001). Discussion: Single-dose vaccination elicited higher neutralizing antibody response and protective immunity in individuals who had recovered from SARS-CoV-2 infection compared with those with no prior exposure. (c) 2021 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc