The scale of the Covid-19 outbreak in Wuhan early this year may have been nearly 10 times the recorded tally, a study conducted by China's public health authorities indicates, leaving the city where the coronavirus first took hold still well short of the immunity required to protect against a potential resurgence.
About 4.4% of those tested were found to have specific antibodies that can fight off the pathogen that causes Covid-19, indicating they were infected sometime in the past, according to a serological survey of more than 34,000 people conducted in April by the Chinese Centre for Disease Control and Prevention. The data was released late last Monday, December 27.
That ratio would suggest that with Wuhan home to about 11 million people, as many as 500,000 residents may have been infected, nearly 10 times more than the 50,000 confirmed Covid-19 cases reported by health authorities in mid-April, when the survey was conducted.
China has been criticized internationally 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 China's accounting of the virus fallout in Wuhan, which was quickly eclipsed by larger outbreaks in Europe and North America. A number of revisions of the case and deaths data added to suspicions China was massaging the numbers.
While the serological data may reignite those claims, it is common for health authorities to under-report cases during an acute outbreak, given that testing capabilities can be limited and hospitals overwhelmed with a sudden surge in patients.
The coronavirus' ability to quietly infect people without making some of them sick until later or even throughout the infection period only exacerbates the problem.
Serological surveillance has been widely used by health professionals around the world to gauge 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.