Patients in New York with severe cases of COVID-19 could start receiving an experimental treatment with blood plasma antibodies as early as next week, a top state health official said Tuesday.

Meanwhile, a test to determine who carries antibodies to COVID-19 is almost ready, the official said.

The body creates antibodies to fight disease and scientists still know relatively little about COVID-19 antibodies.

But blood plasma antibodies were a common treatment in the era before mass-production antibiotics and could work with COVID-19, said Dr. Arthur Fougner, president of the Westbury-based Medical Society of the State of New York, which represents doctors statewide.

“Just because something is old doesn’t make it no good,” he said.

It would not be a cure, but it could save lives, said the state Department of Health official.

“We hope it will result in people having a more rapid recovery and a shorter hospital stay, and less severe outcomes,” the official said. “That’s the hope. That’s what we need to study.”

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With other infectious diseases, the body takes several weeks to produce enough antibodies to help treat others, so the state is first recruiting in places like New Rochelle that had among New York’s earliest cases, the official said.

Volunteer donors would then be tested to confirm they are free of the virus and that they have enough of the right kind of antibodies, and then would donate the plasma. It would take a few weeks to determine how effective the procedure is, the official said. The state expects to receive federal approval for the treatment soon.

Gov. Andrew M. Cuomo has repeatedly expressed optimism that widespread testing for antibodies could be helpful both in understanding how widely COVID-19 has spread — because it would find people who never knew they had carried the virus — and it would allow some who had the virus but no longer do to go back to work. That includes desperately needed health care workers, he said.

The state health department is “in the final stages of validating the antibody test that can be used for that,” the health department official said. “I think it’s really, really close.”

It’s still unknown if people who were infected with the virus and recovered are protected from being infected again, said Dr. Stanley H. Weiss, professor of epidemiology at the Rutgers School of Public Health.

“We have good reason to believe that protective immunity will exist and we all hope that it will exist, although we don't yet know for sure,” Weiss said.

COVID-19 could be like the flu, and a different strain of it could come back next year — or even sooner — so the antibodies may not be effective in the long term, said Dr. Kevin Tracey, CEO and president of the Manhasset-based Feinstein Institutes for Medical Research at Northwell Health.

“The coronavirus might mutate and it might be possible to get twice,” he said. “Nobody knows.”

But the antibodies in the body now presumably would continue to be effective in fighting the current strain of the virus, and “those people should be able to go back to work,” he said.

Mass testing for antibodies is “pretty much the only way to know” how widespread the virus is, because those who carried the virus in the past and recovered would today test negative for COVID-19, but positive for the antibodies, Tracey said.

Retrieving antibodies from people who recovered from COVID-19 also will be helpful in research and could be useful for future anti-viral drugs and in developing vaccines, Weiss said.