Population serology for SARS-CoV-2 is essential to regional and global preparedness
Authors: Huaiyu Tian, Ottar N Bjornstad
Journal: The Lancet Microbe (2020)

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19, poses a tremendous threat to human health.1Chan JFW Yuan S Kok KH et al.A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: a study of a family cluster.Lancet. 2020; 395: 514-523Summary Full Text Full Text PDF PubMed Scopus (5912) Google Scholar, 2Huang C Wang Y Li X et al.Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China.Lancet. 2020; 395: 497-506Summary Full Text Full Text PDF PubMed Scopus (30828) Google Scholar, 3Wu JT Leung K Leung GM Nowcasting and forecasting the potential domestic and international spread of the 2019-nCoV outbreak originating in Wuhan, China: a modelling study.Lancet. 2020; 395: 689-697Summary Full Text Full Text PDF PubMed Scopus (2794) Google Scholar There were more than 4 million confirmed cases and 300 000 reported deaths worldwide as of May 11, 2020. There have been warnings of a major coronavirus pandemic since the SARS outbreak in 2002–04, and in 2020 that threat has been realised. Now we need to consider the challenges ahead; the current prevalence, the incidence of asymptomatic infections, and the true mortality remains unclear. We also need to ascertain the probable effectiveness of current control measures so future strategies can be prioritised accordingly. At the end of 2019, the COVID-19 outbreak was first reported in the city of Wuhan, China, and has since spread worldwide.4Tian H Liu Y Li Y et al.An investigation of transmission control measures during the first 50 days of the COVID-19 epidemic in China.Science. 2020; 368: 638-642Crossref PubMed Scopus (1196) Google Scholar To contain the spread of the disease, a cordon sanitaire was imposed on Wuhan city on Jan 23, 2020, and travel restrictions were subsequently imposed on other cities across Hubei province the next day.5Kraemer MUG Yang C-H Gutierrez B et al.The effect of human mobility and control measures on the COVID-19 epidemic in China.Science. 2020; 368: 493-497Crossref PubMed Scopus (1667) Google Scholar After 61 days of lockdown in Hubei province, the province reopened again on March 25, 2020, and after 76 days of lockdown in Wuhan, the city reopened again on April 8, 2020. The screening of individuals in these areas provides essential information on how immunity, and potentially herd immunity, is shaped in the community that has so far had the longest chain of community transmission but also some of the strongest physical distancing measures. During early-2020, many studies attempted to estimate the reporting rate (or ascertainment rate) of COVID-19 in Wuhan.6Li R Pei S Chen B et al.Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV-2).Science. 2020; 368: 489-493Crossref PubMed Scopus (2145) Google Scholar, 7Pan A Liu L Wang C et al.Association of public health interventions with the epidemiology of the COVID-19 outbreak in Wuhan, China.JAMA. 2020; (published online April 10.)DOI: 10.1001/jama.2020.6130Crossref Scopus (1053) Google Scholar, 8Wu JT Leung K Bushman M et al.Estimating clinical severity of COVID-19 from the transmission dynamics in Wuhan, China.Nat Med. 2020; 26: 506-510Crossref PubMed Scopus (804) Google Scholar Seroprevalence surveys of the general population are key to understanding reporting rates, the underlying number of infections, the build-up of immunity, and to reconstruct chains of transmission of SARS-CoV-2. In The Lancet Microbe, Kelvin To and colleagues9To KK-W Cheng VC-C Cai J-P et al.Seroprevalence of SARS-CoV-2 in Hong Kong and in residents evacuated from Hubei province, China: a multicohort study.Lancet Microbe. 2020; (published online June 3.)https://doi.org/10.1016/S2666-5247(20)30053-7Summary Full Text Full Text PDF Scopus (62) Google Scholar present the results of a seroepidemiological survey of SARS-CoV-2 in the general population in Hong Kong and returnees evacuated from Hubei, China. The investigators enrolled 1938 individuals before and after the COVID-19 pandemic between 2018 and 2020, and 452 asymptomatic Hubei returnees in March, 2020. The study showed that as an emergent virus, SARS-CoV-2 had a seroprevalence of 3·8% among Hubei returnees (17 of 452 returnees); very far from any plausible level of herd immunity. Although the study assessed a small sample—452 of approximately 60 million people in Hubei province—it provides an essential baseline for public health authorities when evaluating the effect of current and future interventions. Judging by patterns of circulation of endemic coronaviruses (HCoV-NL63, HCoV-HKU1, HCoV-229E, and HCoV-OC4),10Killerby ME Biggs HM Haynes A et al.Human coronavirus circulation in the United States 2014–2017.J Clin Virol. 2018; 101: 52-56Crossref PubMed Scopus (194) Google Scholar it is probable that broader immunity might build up in the years ahead. However, To and colleagues' study shows that the current level of immunity is far below the herd immunity threshold and will not appreciably slow future spread, so testing, screening, and contact tracing from symptomatic and asymptomatic infections are still key to stopping further infections. We declare no competing interests. Seroprevalence of SARS-CoV-2 in Hong Kong and in residents evacuated from Hubei province, China: a multicohort studyOur serological data suggest that SARS-CoV-2 is a new emerging virus. The seropositivity rate in Hubei returnees indicates that RT-PCR-confirmed patients only represent a small proportion of the total number of cases. The low seroprevalence suggests that most of the Hong Kong and Hubei population remain susceptible to COVID-19. Future waves of the outbreak are inevitable without a vaccine or antiviral prophylaxis. The role of age-related cross reactive non-neutralising antibodies in the pathogenesis of COVID-19 warrants further investigation. Full-Text PDF Open Access