The total number of Covid-19 infections may be six to 24 times greater than reported, according to a survey of blood samples in six areas across the country conducted by the US Centers for Disease Control and Prevention.
The survey looked for Covid-19 antibodies in blood samples from commercial laboratories – which were collected for reasons unrelated to Covid-19, between March 23 and May 3 – in Connecticut, South Florida, the New York City metro area, Missouri, Utah and western Washington State.
In Connecticut, the survey estimated that 5% of people had antibodies to Covid-19 between April 26 and May 3, which meant there were six times more cases than reported.
In the New York City metro area, that number was 7% of people around late March – 12 times higher than the number of cases reported then. And the survey estimates that 2.65% of Missourians had antibodies in late April. In that case, there were nearly 162,000 cases by April 26 in the state – 24 times higher than the 6,800 reported at the time.
CDC Director Dr. Robert Redfield hinted at preliminary results on Thursday when he told reporters, “The estimates that we have right now … is that’s about 10 times more people have antibody.”
Redfield said that earlier testing efforts may have missed mild and asymptomatic cases, instead focusing on people who were ill in hospitals or nursing homes.
Moving forward: The seroprevalence survey is ongoing, and the CDC says it plans to test about 1,800 samples every three to four weeks from these areas, in addition to four additional states: California, Louisiana, Minnesota and Pennsylvania.
The agency says these samples may not be representative of the total populations in these areas, and the survey didn’t look at risk factors among those sampled – such as a person’s occupation or underlying health conditions.
The survey suggests that while the estimated number of infections may be much greater than official numbers, the vast majority of people have not been infected with the virus.
The jury is still out when it comes to what antibodies mean for immunity to this virus.
“Other studies are planned to learn more about SARS-COV-2 antibodies, including how long they last, whether or not they provide protection against getting infected again, and if you get infected again, whether or not they can make that illness milder,” the agency said.
The CDC adjusted its estimates to account for false positive and false negative results, which may occur frequently in some areas, and cautions against interpreting results on an individual basis for this reason.