Antibody Testing In NYC Reveals 1-in-5 Infection Rate <.5 Fatality Rate

NYTimes | One of every five New York City residents tested positive for antibodies to the coronavirus, according to preliminary results described by Gov. Andrew M. Cuomo on Thursday that suggested that the virus had spread far more widely than known.

If the pattern holds, the results from random testing of 3,000 people raised the tantalizing prospect that many New Yorkers — as many as 2.7 million, the governor said — who never knew they had been infected had already encountered the virus, and survived. Mr. Cuomo also said that such wide infection might mean that the death rate was far lower than believed.

While the reliability of some early antibody tests has been widely questioned, researchers in New York have worked in recent weeks to develop and validate their own antibody tests, with federal approval. State officials believe that accurate antibody testing is seen as a critical tool to help determine when and how to begin restarting the economy, and sending people back to work.

“The testing also can tell you the infection rate in the population — where it’s higher, where it’s lower — to inform you on a reopening strategy,” Mr. Cuomo said. “Then when you start reopening, you can watch that infection rate to see if it’s going up and if it’s going up, slow down.”

The testing in New York is among several efforts by public health officials around the country to determine how many people may have been already exposed to the virus, beyond those who have tested positive. The results appear to conform with research from Northeastern University that indicated that the coronavirus was circulating by early February in the New York area and other major cities.

In California, a study using antibody testing found rates of exposure as high as 4 percent in Santa Clara County — higher than those indicated by infection tests, though not nearly as high as found in New York. Public health officials recently disclosed that a woman in Santa Clara who died on Feb. 6 was infected with the virus.

In New York City, about 21 percent tested positive for coronavirus antibodies during the state survey. The rate was about 17 percent on Long Island, nearly 12 percent in Westchester and Rockland Counties and less than 4 percent in the rest of the state.

State researchers sampled blood from the approximately 3,000 people they had tested over two days, including about 1,300 in New York City, at grocery and big-box stores. The results were sent to the state’s Wadsworth facility in Albany, a respected public health lab.

Dr. Howard A. Zucker, the state health commissioner, said the lab had set a high bar for determining positive results, that it had been given blanket approval to develop coronavirus tests by the Food and Drug Administration and that state officials discussed this particular antibody test with the agency.

He said that while concerns about some tests on the market were valid, the state’s test was reliable enough to determine immunity — and, possibly, send people back to the office.