Anti-SARS-CoV-2 spike immunoglobulinG and immunoglobulinM titers decline as interval from the second inactivated vaccine dose to the onset of illness is prolonged in breakthrough infection patients.

Abstract

Understanding of the early immune response in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) breakthrough infections is limited. Ninety-eight patients with coronavirus disease 2019 (COVID-19) breakthrough infections were divided into two groups, with intervals from receiving the second dose of inactivated vaccine to the onset of illness <60 or ≥60 days. The median lymphocyte count and the median anti-SARS-CoV-2 spike immunoglobulin G (IgG) and immunoglobulin M (IgM) titers were higher in the <60-day interval group compared with the corresponding medians in the ≥60-day interval group (p = 0.005, p = 0.001, and p = 0.001, respectively). The median interleukin-6 (IL-6) level in the <60-day interval group was significantly lower than the median IL-6 level in the ≥60-day interval group (p < 0.001). Our results highlight the different anti-SARS-CoV-2 spike IgG and IgM antibody titers among patients with different intervals from receiving the second dose of inactivated vaccine to the onset of illness.