The scale of the Covid-19 outbreak in Wuhan earlier this year may have been nearly 10 times larger than the recorded count, a study by China’s public health authorities indicates, leaving the city where the coronavirus took hold. the first time still well below the immunity required to protect against a possible resurgence.
About 4.4% of those tested were found to have specific antibodies that can fight the pathogen that causes Covid-19, indicating that they were infected in the past, according to a serological survey of more than 34,000 people conducted in April by the Chinese. Center for Disease Control and Prevention. The data was released Monday night.
That ratio would suggest that with Wuhan in the home of roughly 11 million people, up to 500,000 residents may have been infected, nearly 10 times more than the 50,000 confirmed cases of Covid-19 reported by health authorities in mid-April, when it was reported. conducted the survey. .
China has come under international criticism for its initial handling of the outbreak, which has swept across the world in a global pandemic in the year since the first cases emerged. The United States has raised questions about China’s accounting for the consequences of the virus in Wuhan, which was quickly overshadowed by larger outbreaks in Europe and North America. Various reviews of the case and death data added to suspicions that China was manipulating the numbers.
While serological data can reignite those claims, it is common for health authorities to report fewer cases during an acute outbreak, given that testing capabilities can be limited and hospitals overwhelmed with a surge in patients. The coronavirus’s ability to silently infect people without making some of them sick until later or even during the infection period only compounds the problem.
Serological surveillance has been widely used by healthcare professionals around the world to measure 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 effectively deactivated as a way to contain the outbreak. The antibody positive rate fell to 0.44% for Hubei province overall, which was also placed under a three-month lockdown. Only two people tested positive for the antibody out of 12,000 surveyed 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 the worst-hit city in China remains vulnerable to Covid-19. Epidemiologists say that at least half the population must have been in contact with the virus to even reach the minimum threshold for 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 said in a press release posted on its website.
Antibody positive rates in Spain and Switzerland this spring, for example, were as high as 6.2% and 11%, respectively, China’s CDC said. While those are higher than the 4.4% found in Wuhan, and come before the subsequent waves that swept across Europe, they are still below the threshold for herd immunity.
Since quelling the Hubei outbreak, China has largely contained the coronavirus, with sporadic outbreaks since April being extinguished by aggressive contract tracking and rapid testing of millions of people in a matter of days.
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