The magnitude of the COVID-19 outbreak that emerged earlier this year in Wuhan may have been nearly 10 times larger than the recorded figure , according to a study by China’s public health authorities.
With this, the city where a case of the SARS-CoV-2 virus was reported for the first time is still at a level of immunity much lower than necessary to protect itself against a possible resurgence.
It was discovered that about 4.4 percent of the people tested had specific antibodies that can fight the pathogen that causes COVID-19, that is, at some point they were infected, this according to a serological study done to more than 34 thousand people in April by the Chinese Center for Disease Control and Prevention
This index would suggest that, considering that about 11 million people live in Wuhan , up to 500 thousand inhabitants may have contracted COVID-19, almost 10 times more than the 50 thousand cases of contagion reported by health authorities in mid-April, when the study was conducted.
China has come under international criticism for its initial handling of the outbreak, which has spread around the world in a global pandemic in the year since the first cases emerged.
The United States has raised questions about the numbers of cases of the pathogen in Wuhan reported by China, which were quickly dwarfed by larger outbreaks in Europe and North America. A series of revisions of contagion and death data added to suspicions that Beijing was manipulating the figures.
While serologic data may reignite those allegations, it is common for health authorities to report lower case numbers during an acute outbreak, as testing capacities may be limited and hospitals could be overwhelmed with a sudden surge of patients.
The ability of the new coronavirus to silently infect people and that some of them do not have symptoms until later or even do not manifest them during the entire period of infection, only exacerbates the problem.
Serological surveillance has been widely used by healthcare professionals around the world to assess the true scale of epidemics, from COVID-19 to AIDS and hepatitis . The prevalence of disease derived from such studies can guide mitigation and vaccination efforts.
China’s CDC survey showed a much smaller impact of the virus outside of Wuhan, which was isolated as a way to contain the outbreak. The antibody positivity rate fell to 0.44 percent for the broader area of Hubei province, which was also subjected to a three-month lockdown .
Only two people tested positive for the antibody among the 12,000 tested in six other Chinese cities and provinces, including Beijing, Shanghai and Guangdong, suggesting an extremely low prevalence of the virus in the rest of the country.
The results for Wuhan mean that even China’s worst-hit city remains vulnerable to the pandemic. Epidemiologists note that at least half of the population must have come into contact with the virus to reach the minimum threshold for herd immunity (herd immunity), but the city’s infection rate is generally in line with those found in other countries after the first wave of coronavirus infections, China’s CDC noted in a press release posted on its website.
Antibody positivity rates in Spain and Switzerland this spring, for example, were as high as 6.2 and 11 percent, respectively, China’s CDC noted. Although these figures are higher than the 4.4 percent found in Wuhan and correspond to before the subsequent waves that have swept through Europe, they still do not reach the threshold for herd immunity.
Since controlling the Hubei outbreak, China has largely contained the new coronavirus, as sporadic outbreaks that have emerged since April have been suppressed through strong contact tracing and rapid testing of millions of people in a matter of days.