Shanghai’s unusually high share of asymptomatic COVID-19 infections has raised suspicions that the city classifies cases as mildly symptomatic, a different counting method from the rest of the country, comments from a local health adviser adding to the doubts.
Authorities in China’s financial hub have ordered a lockdown in response to the country’s worst outbreak since the outbreak of the Wuhan virus in late 2019.
Shanghai had more than 20,000 new cases on April 7, but the asymptomatic rate stood at around 97%, far higher than anywhere else in the world, where it is closer to 50%.
Fu Chen, head of the municipal center for disease control and prevention, said in a written response to questions from Reuters that Shanghai’s rapid surveillance tests were contributing to high asymptomatic numbers by detecting infections earlier.
He also said high vaccination rates also have an impact, as people vaccinated are less likely to show symptoms.
Fu did not say directly that Shanghai used less stringent diagnostic criteria, but he suggested the numbers in the rest of China would be comparable if “mildly symptomatic” cases were included in the tally of asymptomatics.
“Recently, a press conference of the Joint Prevention and Control Mechanism of the State Council also said that the proportion of mildly symptomatic and asymptomatic infections in hospitals nationwide is over 95 percent,” Fu noted.
The city government did not immediately respond to a request for comment on whether or not Shanghai uses different diagnostic standards than those used elsewhere.
In China, asymptomatic cases are defined as those who test positive for the coronavirus but have no “relevant” clinical manifestations, Fu said.
National guidelines define asymptomatic cases as those who test positive but have no clinical symptoms such as fever, and no signs of COVID in their lungs, as determined by a CT scan.
Asymptomatic cases are reclassified if symptoms appear later.
“Mildly symptomatic” cases are those with mild symptoms but no signs of pneumonia after a chest CT scan.
According to national standards, determining an asymptomatic case requires a chest CT scan, which would put Shanghai’s medical system under immense pressure given the scale of the current outbreak. It’s unclear exactly how many asymptomatic cases in Shanghai or elsewhere have undergone lung CT scans.
Paul Hunter, professor of medicine at the University of East Anglia, told Reuters it would be “absolutely crazy” to have everyone who tested positive scanned.
In northeast China’s Jilin Province, site of another major outbreak, asymptomatic cases have accounted for less than half of reported infections, although that figure has risen steadily to around 60% in recent years. days.
But according to Reuters calculations, if mildly symptomatic cases from Jilin are added to the tally of asymptomatics, the share would rise to over 96% – similar to the asymptomatic figures from Shanghai.
Unlike other countries, China separately counts asymptomatic cases, even though all COVID-positive cases are isolated in central quarantine facilities, whether or not they show symptoms.
IRRESPONSIBLE
Chinese netizens have accused Shanghai of putting mildly symptomatic cases in the asymptomatic column to allay public concerns about the potency of the highly transmissible Omicron variant. The city had initially used a more surgical approach to curbing infections in hopes of avoiding more onerous measures.
“Shanghai’s definition of ‘asymptomatic’…has not only made national statistics meaningless, but also the delineation of risk areas,” said a Weibo user writing under the username Chairman Rabbit. .
Foreign experts also remain skeptical, with epidemiologist Michael Osterholm from the University of Minnesota saying the ratio “simply doesn’t make biological sense”.
“At this stage, I simply dispute the authenticity of the data”.
Fu said Shanghai’s high proportion of asymptomatic cases also reflected the reduced potency of the Omicron, and he added that most cases were in relatively young, more resilient people who were more likely to have been vaccinated.
He noted that 22 million residents had already received two vaccines and more than 11 million had received boosters, making them less vulnerable to the disease.
“Mass immunity is getting stronger,” he said.