COVID-19 may have continued to spread silently in Wuhan, China, during the spring of 2020, even after official government records suggested the coronavirus had been eliminated, a new study suggests.
SARS-CoV-2, the virus that causes COVID-19, was the first discovered in Wuhan in December 2019, and the city soon became the epicenter of what would become the COVID-19 pandemic. Cases peaked in Wuhan in February 2020, but soon declined rapidly, with only a few cases reported in late March. In early April, the the city blockade was over, and later that month, Wuhan was declared free of the coronavirus.
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 collected in China – mainly in Wuhan – between March 6 and May 3, 2020. All of these participants were healthy and were undergoing tests before returning to work, the researchers said.
Blood samples were tested for antibodies against SARS-CoV-2. Specifically, the researchers looked for both IgG antibodies, a type of long-lasting antibody that suggests 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 any 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%.
Furthermore, the researchers found that the IgM positivity rate – indicating an active or recent infection – in Wuhan was almost 0.5%, compared with 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, the researchers estimated that thousands of people were asymptomatically infected during this period.
“We concluded that … a large number of asymptomatic carriers of SARS-CoV-2 existed after the elimination of clinical cases of COVID-19 in the city of Wuhan,” wrote the researchers.
Based on the study’s antibody numbers, the researchers estimated that in Wuhan, a city of about 10 million, about 168,000 people had been infected in Wuhan at that time – more than the approximately 50,000 reported cases.
The authors noted that from May 14 to June 1, officials in Wuhan conducted mass tests of COVID-19 on 9.9 million people and found an asymptomatic infection rate of just 0.3 per 10,000 people based on tests of PCR for SARS-CoV-2 genetic material
But the rate found in the current study, based on the IgM test, was hundreds of times higher, the researchers said. This discrepancy may be due to a number of factors, including increased sensitivity of blood antibody tests compared to the PCR test and previous collection dates in the current study compared to surveillance tests done by city officials, the researchers said. researchers.
Originally published on Live Science.