The latest study of Chinese infected by COVID-19 in Wuhan -- the first global epicenter of the disease -- confirms mass vaccinations will be needed to reach herd immunity and to prevent further resurgences of the pandemic.
Published in The Lancet Friday, the observational study of 9,542 people revealed fewer than one in 10, or only 6.9% of Wuhan residents, carried COVID-19 antibodies in their bloodstream in April, or four months after COVID-19 first appeared in Wuhan. In addition, 82% of these people had asymptomatic infections.
Only 40% tested positive for the neutralizing antibodies needed to prevent future infections. These neutralizing antibodies lasted for up to nine months regardless of whether individuals had symptomatic or asymptomatic disease.
The data shows a large proportion of Wuhan's population remained uninfected months after the outbreak, confirming the absolute necessity of mass vaccination to reach herd immunity.
"Even at the epicenter of the pandemic, with more than 50,000 confirmed cases as of April 8, 2020, the estimated seroprevalence (bloodborne evidence of infection) in Wuhan remains low," said study author Dr. Chen Wang, who is also president of the Chinese Academy of Medical Sciences and Peking Union Medical College.
Wang said this outcome means vaccinations will be required to promote herd immunity. He pointed out assessing the proportion of the population that infected with SARS-CoV-2 (the virus that causes COVID-19) and who are immune is of utmost importance for determining effective prevention and control strategies to reduce the likelihood of future resurgence of the pandemic.
"Given that individuals with mild infections might not seek medical care and that asymptomatic individuals are not usually screened, there may be large discrepancies between the reported COVID-19 cases, and actual infected cases, which has been proven by the experiences and data from other countries," he noted.
"Even at the epicentre of the pandemic in China, with more than 50,000 confirmed cases as of April 8, 2020, the estimated seroprevalence in Wuhan remains low, and around 40% of people with antibodies developed neutralizing antibodies, suggesting there is still lack of immunity in the population."
The study said understanding seroprevalence and how antibody levels change over time in Wuhan will help inform their vaccination strategy. Ita findings indicatethat mass vaccination is needed to protect against future resurgences of SARS-CoV-2.
The finding that antibody levels in asymptomatic patients are lower than those in confirmed patients and symptomatic cases will help facilitate precise COVID-19 infection prevention in the future, said co-author Dr. Ren Lili.
"Little is known of the durability of immune responses against COVID-19 over a long period," said Ren, who is from the Institute of Pathogen Biology under the Chinese Academy of Medical Sciences and Peking Union Medical College.
"In our study, we found that the proportion of participants with antibodies against the virus was sustained for at least nine months. Importantly, we found that neutralizing antibody titers remained stable for at least nine months."
The first long-term seroprevalence survey in Wuhan tested COVID-19 antibodies in residents living across all 13 districts after the city's lockdown was lifted in April 2020. Follow-up blood-sample tests were conducted in June and between October and December to examine if antibodies were present.
