Seroprevalence of SARS-CoV-2 in Hong Kong returnees – Authors' reply
Authors: Kelvin Kai-Wang To, Kwok-Yung Yuen
Journal: The Lancet Microbe (2020)

We are grateful for the useful comments of William P Hanage and colleagues. We admitted the limitations of our study, in which we used a relatively small and geographically non-random cohort of 452 Hong Kong Special Administration Region (HKSAR) residents evacuated from Hubei Province as a representation of the situation in Hubei Province in March, 2020. Therefore, we can only prudently include the possible implications of our findings in the discussion. Although we acknowledge that Hanage and colleagues estimated a higher case fatality rate on the basis of data from Wuhan city, the number of deaths stated in their letter, 3689, is much higher than those reported in early March when the blood samples were collected from the returnees. According to data from the Health Commission of Hubei Province, there were only 2227 deaths in Wuhan city as of March 1, 2020, and 2469 deaths in Wuhan city as of March 15, 2020.1Health Commission of Hubei ProvinceUpdate of the situation of COVID_19 in Hubei Province on March 1, 2020.http://wjw.hubei.gov.cn/fbjd/dtyw/202003/t20200302_2167398.shtmlDate accessed: June 16, 2020Google Scholar, 2Health Commission of Hubei ProvinceUpdate of the situation of COVID-19 in Hubei Province on March 15, 2020.http://wjw.hubei.gov.cn/fbjd/dtyw/202003/t20200316_2182353.shtmlDate accessed: June 16, 2020Google Scholar Therefore, the case fatality rate in Wuhan would probably be lower than that estimated by Hanage and colleagues. In the discussion of our study, we estimated the number of seropositive individuals in Hubei province, and, in particular, Wuhan city on the basis of seroprevalence rates among evacuees returning to HKSAR. Limited by the relatively small sample size, the 95% CI of the seroprevalence rate is large, and therefore we did not do a further statistical analysis on the mortality rate on the basis of our seroprevalence data, and did not calculate a separate mortality rate on Wuhan city. Rather, our estimate aimed to provide the reader with a sense of the magnitude of the mortality when compared with that of pandemic influenza. Furthermore, since only 88 individuals returning from outside Wuhan city were included, we did not separate the analysis for other cities. Further studies in other parts of Hubei province will be needed to better understand the seroprevalence rates in different geographical areas. Compared with regions in other countries affected by the ongoing COVID-19 pandemic, our study found that Hubei Province and HKSAR have relatively low seroprevalence rates which were probably the result of successfully implemented stringent control measures in these localities. As Hanage and colleagues have pointed out, our study showed that the first wave of COVID-19 did not result in population immunity. This low herd immunity among our population in Hubei Province and HKSAR might allow a second wave of COVID-19 if control measures were overly loosened before an effective vaccine is available. 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 AccessSeroprevalence of SARS-CoV-2 in Hong Kong returneesWe read with interest Kelvin Kai-Wang To and colleagues' paper, published in The Lancet Microbe, about the prevalence of antibodies to SARS-CoV-2 in returnees to Hong Kong from Hubei province in China.1 We agree with the authors' conclusion that the reported seroprevalence of 4% indicates that the initial surge of infection did not result in population immunity. The study generated considerable social media interest for a finding that the authors reported in the discussion. The authors extrapolated from the estimated prevalence to calculate an infection fatality rate (IFR) for Hubei province. Full-Text PDF Open Access