Antibody seroprevalence in the epicenter Wuhan, Hubei, and six selected provinces after containment of the first epidemic wave of COVID-19 in China

Background: China implemented containment measures to stop SARS-CoV-2 transmission in response to the COVID-19 epidemic. After the first epidemic wave, we conducted population-based serological surveys to determine extent of infection, risk factors for infection, and neutralization antibody levels to assess the real infections in the random sampled population.Methods: We used a multistage, stratified cluster random sampling strategy to conduct serological surveys in three areas - Wuhan, Hubei Province outside Wuhan, and six provinces selected on COVID-19 incidence and containment strategy. Participants were consenting individuals >1 year old who resided in the survey area >14 days during the epidemic. Provinces screened sera for SARS-CoV-2-specific IgM, IgG, and total antibody by two lateral flow immunoassays and one magnetic chemiluminescence enzyme immunoassay; positive samples were verified by micro-neutralization assay.Findings: We enrolled 34,857 participants (overall response rate, 92%); 427 were positive by microneutralization assay. Wuhan had the highest weighted seroprevalence (4.43%, 95% confidence interval [95%CI]=3.48%-5.62%), followed by Hubei-ex-Wuhan (0.44%, 95%CI=0.26%-0.76%), and the other provinces (<0.1%). Living in Wuhan (adjusted odds ratio a0R-13.70, 95%CI= 7.91-23.75), contact with COVID-19 patients (aOR=7.35, 95%CI=5.05-10.69), and age over 40 (aOR=1.36, 95%CI=1.07-1.72) were significantly associated with SARS-CoV-2 infection. Among seropositives, 101 (24%) reported symptoms and had higher geometric mean neutralizing antibody titers than among the 326 (76%) without symptoms (30+2.4 vs 15+2.1, p<0.001).Interpretation: The low overall extent of infection and steep gradient of seropositivity from Wuhan to the outer provinces provide evidence supporting the success of containment of the first wave of COVID-19 in China. SARS-CoV-2 infection was largely asymptomatic, emphasizing the importance of active case finding and physical distancing. Virtually the entire population of China remains susceptible to SARS-CoV-2; vaccination will be needed for long-term protection. (C) 2021 The Author(s). Published by Elsevier Ltd.