Age-Stratified Seroprevalence of SARS-CoV-2 Antibodies before and during the Vaccination Era, Japan, February 2020–March 2022

Abstract

despite the development of effective vaccines and therapeutics, >500 million persons had been infected with the virus and ≈6 million had died (1). In Japan, with a population of ≈125 million, the reported numbers are ≈7 million infections and ≈30,000 deaths by that time (2); however, the actual number of infected persons must be higher than the reported figure because not all infected persons undergo diagnostic testing.A serologic survey can retrospectively find persons who have been infected with the virus (3). Antibodies against the SARS-CoV-2 spike protein are generated by vaccination and natural infection. In contrast, antibodies against other components of the virus, such as the nucleoprotein, represent a history of SARS-CoV-2 natural infection but not vaccination with the COVID-19 vaccines currently available in Japan. Analyses of seroprevalence in several countries have revealed that the actual incidence of SARS-CoV-2 infection is much higher than the reported COVID-19 cases (3). For example, in the United States, the seroprevalence of antibodies against the SARS-CoV-2 nucleoprotein ranged from 3% to 10% in 2020 (4-7), and this number reached roughly 20%-60% in 2021 (8,9). However, diagnostic tests confirmed only a Age-Stratified Seroprevalence of SARS-CoV-2 Antibodies before and during the Vaccination Era, Japan,

Seroprevalence of severe acute respiratory syndrome coronavirus 2 N antibodies between December 2021 and march 2023 in Japan

“…Convalescent sera from patients with laboratory-confirmed COVID-19, which were collected previously [ 2 ], were used as positive controls, and residual serum samples collected in Nov 2019 in Japan were used as negative controls.…”

“…Residual serum or plasma samples were collected in the Tokyo metropolitan area (n = 7604) and Sapporo (n = 3354), respectively. The samples collected in December 2021 and March 2022 were also used in a previously study [ 2 ].…”

“…As of May 2023, 760 million cases including 6.9 million deaths have been reported to the World Health Organization (https://covid19.who.int/). The threat of SARS-CoV-2 is subsiding as most people have acquired sufficient antibodies through vaccination and/or infection to prevent severe COVID-19; more than 80% of the populations of major industrialized countries have antibodies against the S protein induced by vaccination and/or infection [1][2][3][4][5]. In contrast, the seroprevalence of antibodies against the N protein elicited by SARS-CoV-2 infection ranged from 44.4% to 80.2% in the United States, England, Spain, Slovenia, Switzerland, and Thailand between March and November 2022 after the emergence of the omicron variants [3,4,[6][7][8][9][10].…”

Seroprevalence of SARS-CoV-2 antibodies in dogs and cats during the early and mid-pandemic periods in Japan

“…Antibodies against SARS-CoV-2 were examined by use of an ELISA as previously reported [ 31 , 32 ]. Briefly, 96-well Maxisorp microplates (Nunc) were incubated with 2 μg/ml of recombinant receptor-binding domain (RBD) or ectodomain (S) of the spike protein, the N protein (N) derived from Wuhan-Hu-1 (Gen-Bank, accession no.…”