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COVID-19 may have continued to spread silently in Wuhan, China in the spring of 2020, even after official government counts suggested the coronavirus had been eradicated, a new study suggests.
SARS-CoV-2, the virus responsible for COVID-19, was the first discovered in Wuhan in December 2019, and the city quickly became the epicenter of what would become the COVID-19 pandemic. Cases peaked in Wuhan in February 2020, but declined rapidly, with only a few cases reported in late March. In early April, the lockdown of the city was over, and later that month Wuhan was declared coronavirus-free.
But the new study, published Thursday, January 7 in the journal PLOS Neglected Tropical Diseases, tells a different story. The researchers, from Wuhan University, analyzed more than 63,000 blood samples taken in China – mainly Wuhan – between March 6 and May 3, 2020. All of these participants were in good health and undergoing screening before returning. at work, the researchers said.
Blood samples were tested for antibody against SARS-CoV-2. Specifically, the researchers looked for both IgG antibodies, a type of long-lasting antibody suggesting a previous infection with SARS-CoV-2, and IgM antibodies, a relatively short-lived antibody that suggests a current or recent infection with the virus.
In Wuhan, the percentage of participants with either of these antibodies was 1.7%. This is much higher than the percentage seen in areas outside Hubei Province (which includes Wuhan), which was around 0.4%.
In addition, the researchers found that the rate of IgM positivity – indicating active or recent infection – in Wuhan was nearly 0.5%, compared to 0.07% in other parts of China.
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Based on the level of IgM antibodies observed in Wuhan in the spring of 2020, researchers estimated that thousands of people were asymptomatically infected during this time.
“We conclude that a large amount of asymptomatic carriers of SARS-CoV-2 existed after the elimination of clinical cases of COVID-19 in Wuhan city,” the researchers wrote.
Based on the antibody numbers in the study, the researchers estimated that in Wuhan, a city of around 10 million people, around 168,000 people had been infected overall in Wuhan at that time, i.e. more than the roughly 50,000 reported cases.
The authors noted that from May 14 to June 1, Wuhan officials performed COVID-19 mass testing on 9.9 million people and found an asymptomatic infection rate of only 0.3 per 10,000 people on the basis of PCR testing for genetic material of SARS-CoV-2.
But the rate found in the current study, based on IgM tests, was hundreds of times higher, the researchers said. This discrepancy could be due to several factors, including greater sensitivity of blood antibody tests compared to PCR tests and earlier collection dates in the current study compared to surveillance tests performed by city officials. , the researchers said.
Originally posted on Live Science.
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