Anti-SARS-CoV-2 IgG antibody after the second and third mRNA vaccinations in staff and residents in a nursing home with a previous COVID-19 outbreak in Niigata, Japan

Abstract

This study measured IgG antibody titers against spike (S) and nucleocapsid (N) proteins of SARS-CoV-2 before vaccination and after the second and third doses of an mRNA vaccine in staff and residents of a nursing home in Niigata, Japan. The study included 52 staff members, of whom six (11.5%) were previously infected with SARS-CoV-2, and 32 older residents, of whom 22 (68.8%) were previously infected. All participants received the first two doses in April–July 2021 and a third dose in January–March 2022. In staff, the median anti-S antibody titers (interquartile range) in previously infected and SARS-CoV-2-naïve individuals before vaccination were 960 (592–1,926) and 0.5 (0.0–2.1) arbitrary units (AU)/mL. Anti-S antibody titers 5 months after the second and third doses in previously infected staff were 7,391 (5,230–7,747) and 10,195 (5,582–13,886) AU. In residents, the median anti-S antibody titers in previously infected and naïve individuals before vaccination were 734 (425–1,934) and 1.1 (0.0–3.1) AU/mL. Anti-S antibody titers at 5 months after the second and third doses in previously infected residents were 15,872 (9,683–21,557) and 13,813 (6,689–20,839) AU/mL; however, there were no significant differences in titers between the second and third doses in previously infected residents. Anti-N antibody titers were higher in previously infected than naïve individuals, and titers decreased chronologically.