After witnessing the first explosion of COVID-19 cases last year, Wuhan in Central China was thought to have the outbreak under control by springtime, with new infections reportedly dropping to zero by March 19, 2020. However, while it seemed that the virus had temporarily been quashed by late-April, antibody tests now show that the outbreak was continuing to silently linger around this time.
New research by scientists at Wuhan University suggests COVID-19 was silently spreading between thousands of people in the city while the infection appeared to be under control in springtime.
By their workings, up to 168,000 Wuhan residents may have been infected with the virus between March and early-May. Considering there were a total of 50,340 reported cases officially logged in Wuhan, the researchers argue at least two-thirds of the total number of cases in Wuhan were asymptomatic and "slipped under the radar."
Published in the journal PLOS Neglected Tropical Diseases this week, the study looked at levels of antibodies in blood samples collected between March 6 and May 3 2020 from 63,107 people in Wuhan, other cities in Hubei Province, and other places in China. All these people were seemingly healthy and took rapid antibody tests before returning to work. The tests looked for both positive IgG antibodies, which indicate a previous infection, and IgM antibodies, which indicate a current or recent infection.
The researchers found that the percentage of people with SARS-CoV-2 antibodies was significantly higher in Wuhan compared to other parts of China. While the average antibody positivity was 0.38 percent across China, at least 1.68 percent of tested people in Wuhan had the antibodies.
Furthermore, at least 0.46 percent in Wuhan were found to possess IgM antibodies, which the researchers argue would mean 168,000 people in the city were infected between March and May 2020, although most suffered no symptoms and went otherwise undetected. This suggests the real number of COVID-19 cases in Wuhan was potentially three times higher than the number of reported cases.
“We estimated that 168,000 people were infected with SARS-CoV-2 during the COVID-19 epidemic in the city. Wuhan City has reported 50,340 hospitalized COVID-19 patients as of May 19, 2020, indicating that only one-third [of] SARS-CoV-2 infected persons need to be hospitalized and at least 2/3 [of] infected persons were asymptomatic in the city,” reads the study.
Another recent antibody study by the Chinese Centre for Disease Control and Prevention has gone even further to suggest that up to half a million people in Wuhan were likely to be infected by the virus. With a new study out today suggesting over half of COVID cases are spread by people without symptoms, true figures are likely a long way off.
Earlier this year, Wuhan and Hubei authorities found themselves in hot water over the way they recorded COVID-19 infections and mortality, with some speculating they had missed or failed to report many of the early infections. This led them to revise their mortality rate upwards of 50 percent in April 2020. However, it appears that the number of cases in Wuhan is still based on the number of hospitalized patients, meaning those that were infected with COVID-19 but not hospitalized might be missing from the count.
Much of the initial phase of the COVID-19 pandemic remains hazy. However, as studies like this show, it's still possible to piece together parts of the story.
For more information about COVID-19, check out the IFLScience COVID-19 hub where you can follow the current state of the pandemic, the progress of vaccine development, and further insights into the disease.