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BEIJING – More than eight out of 10 people in the Chinese city of Wuhan who tested positive for Covid-19 antibodies were asymptomatic for the disease, and less than half developed neutralizing antibodies that protect against future infection, a new Chinese study shows.
The study, which the researchers said was the first long-term Covid-19 antibody prevalence study from the epicenter of the outbreak in China, also found that 6.9 percent had Covid-19 antibodies, indicating a prior infection.
The figure indicates that about 765,000 people could have been infected in Wuhan, a city of 11.08 million, confirming reports that the infection figures were much higher than the official count of around 50,000 cases.
An earlier study by the Chinese Center for Disease Control and Prevention in December found an antibody prevalence rate of 4.43 percent in Wuhan.
The latest study, published in the medical journal The Lancet last Saturday (March 20), looked at the seroprevalence, or prevalence of antibodies, of 9,542 people in Wuhan from April to December last year.
The study was conducted by a group of Chinese researchers from a variety of medical and research institutions, including the Chinese Academy of Medical Sciences and the Peking Union Medical College.
The researchers had found that a large majority, or 82 percent, of those who tested positive for antibodies had no symptoms, noting that this was “much higher than the average proportions of 40 to 45 percent that are reported. have been reported all over the world. “
The study’s lead author, Dr. Wang Chen of the Chinese Academy of Medical Sciences, said the discrepancy is unlikely to be due to recall bias on the part of study participants, given the authorities’ efforts to identify cases and encourage residents to record their symptoms.
The researchers had also found that only about 40 percent of people with antibodies had developed neutralizing antibodies, the kind that protect against future infection, and levels of those antibodies were higher in people who showed symptoms.
The levels of these neutralizing antibodies were stable for at least nine months, they found.
Dr. Wang said that assessing the proportion of the population immune to Covid-19 was “of utmost importance in determining effective prevention and control strategies.”
The researchers said the low level of immunity, even at the epicenter of the Wuhan pandemic, underscores the importance of vaccines and that “mass vaccination is needed to protect the herd and prevent a resurgence of the epidemic.”
Dr. Jin Dong-Yan, a professor of virology at the University of Hong Kong, said the study was important and adds to the growing knowledge that actual infection figures were much higher in Wuhan than official figures.
But he also pointed out that while the study found that only 40 percent of those infected had developed neutralizing antibodies, that does not mean that those without them had a lack of immunity to the virus.
“It is very possible that they have memory B and T cells against Sars-CoV-2,” he said, referring to the virus that causes Covid-19.
Memory B and T cells are long-lived cells that develop after a previous infection and remain dormant until the pathogen is re-infected, after which they trigger a rapid immune response.
“When these people are infected or vaccinated, if they develop neutralizing antibodies quickly, they could also be fully protected against Sars-CoV-2,” said Professor Jin.
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