Serum neutralization of SARS coronavirus 2 Omicron sublineages BA.1 and BA.2 and cellular immune responses 3 months after booster vaccination

Objectives: We investigated serum neutralizing activity against BA.1 and BA.2 Omicron sublineages and T cell response before and 3 months after administration of the booster vaccine in healthcare workers (HCWs). Methods: HCWs aged 18-65 years who were vaccinated and received booster doses of the BNT162b2 vaccine were included. AntieSARS coronavirus 2 IgG levels and cellular response (through interferon gamma ELISpot assay) were evaluated in all participants, and neutralizing antibodies against Delta, BA.1, and BA.2 were evaluated in participants with at least one follow-up visit 1 or 3 months after the administration of the booster dose. Results: Among 118 HCWs who received the booster dose, 102 and 84 participants attended the 1-month and 3-month visits, respectively. Before the booster vaccine dose, a low serum neutralizing activity against Delta, BA.1, and BA.2 was detectable in only 39/102 (38.2%), 8/102 (7.8%), and 12/102 (11.8%) participants, respectively. At 3 months, neutralizing antibodies against Delta, BA.1, and BA.2 were detected in 84/84 (100%), 79/84 (94%), and 77/84 (92%) participants, respectively. Geometric mean titres of neutralizing antibodies against BA.1 and BA.2 were 2.2-fold and 2.8-fold reduced compared with those for Delta. From 1 to 3 months after the administration of the booster dose, participants with a recent history of SARS coronavirus 2 infection (n = 21/84) had persistent levels of S1 reactive specific T cells and neutralizing antibodies against Delta and BA.2 and 2.2-fold increase in neutralizing antibodies against BA.1 (p 0.014). Conversely, neutralizing antibody titres against Delta (2.5-fold decrease, p < 0.0001), BA.1 (1.5-fold, p 0.02), and BA.2 (2-fold, p < 0.0001) declined from 1 to 3 months after the administration of the booster dose in individuals without any recent infection. Discussion: The booster vaccine dose provided significant and similar response against BA.1 and BA.2 Omicron sublineages; however, the immune response declined in the absence of recent infection. Enagnon Kazali Alidjinou, Clin Microbiol Infect 2023;29:258.e1-258.e4 (c) 2022 European Society of Clinical Microbiology and Infectious Diseases. Published by Elsevier Ltd. All rights reserved.