More than 2 million New Yorkers had been infected with Covid-19 by the end of March – about 10 times the official count, according to a new study.
State data, however, shows only about 189,000 cases by the end of March. That means about 1.8 million cases potentially went undetected.
Why cases may have been undercounted: There are several reasons why those cases were not detected, said study coauthor David Holtgrave, dean of the School of Public Health at the University at Albany.
Some infected people may have had no symptoms, or only mild symptoms, and so never went to the doctor, Holtgrave said. Others might have wanted to get tested but couldn’t find a doctor to test them, given the shortage of tests in February and March.
In the study, researchers drew blood from more than 15,000 New York adults and found that about 14%, or 1 out of 7, had antibodies to the virus, which means they had previously been infected. The researchers extrapolated that number to the entire population.
On herd immunity: While the 14% infection rate was higher than previously thought, it’s still not high enough to confer herd immunity, Holtgrave said.
Herd immunity is when a community has a sufficiently high proportion of people who are immune to a disease so that the disease is unlikely to spread. These are the full results of New York's antibody survey, some of which New York Gov. Andrew Cuomo has previously mentioned.
The data also shows that communities of color were disproportionately infected. Among those who had antibodies, 30% were Hispanic and 22% were black, which is higher than their proportions in the New York population.
The study was coauthored by officials at the New York Department of Health, and posted on the pre-print server MedRXiv.org, which means it wasn’t peer reviewed or published in a medical journal.