When it comes to figuring out the impact that the global pandemic has had on the human population, there is a large area of uncertainty: how many people have been infected with SARS-CoV-2 inadvertently?
We know that people who have contracted the coronavirus do not necessarily show any signs of it (about 40 percent of cases are believed to be asymptomatic) and that puts a question mark on the official figures that have been collected so far.
To try to establish how many unreported infections we might have missed, the researchers looked at the results of blood tests of 61,910 people who did not believe they had contracted the virus, to see if any antibodies were linked to fighting SARS-CoV. -2, the virus that causes COVID-19 disease.
In the entire sample, 4,094 people had antibodies related to a SARS-CoV-2 infection, about 6 or 7 people out of 100 people. Extrapolating that fraction to the entire population, the US may have had around 16 million asymptomatic or undiagnosed cases as of September 30, 2020, when the blood tests were done.
To put it another way: twice as many cases as were actually recorded in the US by October 2020.
“Officially reported case counts may substantially underestimate the overall burden of infection in the United States,” the researchers write in their article. “Viral serologic tests can provide a more accurate estimate of the cumulative prevalence of the disease.”
The team notes certain limitations in their work, including the fact that the participants self-reported their health status, and the sample was “an unbalanced representation of the US population by age, sex, and place of residence.”
However, their results highlight the need to continue surveillance of the disease throughout the population, and it makes sense, given that the virus does not always reveal itself even in people who have it. Another antibody study published last year showed that the presence of antibodies to SARS-CoV-2 varies widely among US jurisdictions, from less than 1 percent to 23 percent of the region’s population.
That variation occurs between age groups and genders, as well as geographic location, further complicating the task of trying to control how many people have been affected by a SARS-CoV-2 infection.
Another question that might need a more definitive answer is how many antibodies are produced in asymptomatic cases. In these people, the body may not need to fight as hard to fight the virus and therefore produce less of the necessary antibodies, or at least lose them more quickly.
Not having any symptoms of COVID-19 may be better for the person who actually has the virus, but it makes it difficult to track and contain the coronavirus. Asymptomatic carriers can still transmit the virus, almost undetected.
“Understanding … the true prevalence of antibodies in the community would be helpful in understanding how likely we are to continue to have outbreaks,” said infectious disease physician Sara Keller of the Johns Hopkins University School of Medicine who was not involved in the study. the Los Angeles Times.
Ultimately, the more data we have on this harmful coronavirus, from case numbers to transmission rates, the better we can control it, and this latest study will help with that as we seek to get life back to normal.
The research has been published in Open JAMA network.