Comparable humoral and cellular immunity against Omicron variant BA.4/5 of once-boosted BA.1/2 convalescents and twice-boosted COVID-19-naïve individuals

The fourth vaccination dose confers additional protective immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in individuals with no prior coronavirus disease-19 (COVID-19). However, its immunological benefit against currently circulating BA.4/5 is unclear in individuals who have received a booster shot and been infected with Omicron variant BA.1/2. We analyzed immune responses in whom had been boosted once and did not have COVID-19 (n = 16), boosted once and had COVID-19 when BA.1/2 was dominant in Korea (Hybrid-6M group, n = 27), and boosted twice and did not have COVID-19 (Vx4 group, n = 15). Antibody binding activities against RBD_{o BA.1} and RBD_{o BA.4/5}, antigen-specific memory CD4⁺ and CD8⁺ T-cell responses against BA.4/5, and B-cell responses against SARS-CoV-2 wild-type did not differ statistically between the Hybrid-6M and Vx4 groups. The humoral and cellular immune responses of the Hybrid-6M group against BA.4/5 were comparable to those of the Vx4 group. Individuals who had been boosted and had an Omicron infection in early 2022 may not have high priority for an additional vaccination.