COVID-19 blood tests are emerging as a keystone in efforts to return to work and school and to end social distancing.
Different from the nasal swab tests that confirm whether someone is presently infected with the coronavirus, the blood tests are designed to determine whether individuals had previously been infected and conquered the disease.
People who have weathered the virus may be immune from new infection and can become a vanguard for resuming social and economic activity.
New York Gov. Andrew M. Cuomo on Sunday announced plans to test the blood of 3,000 people across the state to determine the percent of the population that recovered from the virus.
The test, known as a “serosurvey,” will draw participants from supermarkets around the state, including one in Nassau County. The World Health Organization and the National Institutes of Health are rolling out serosurveys on the global and national levels as well.
Unlike the nasal swab test, which looks for the coronavirus in molecules gathered from the nose, the blood tests search for so-called antibodies to the coronavirus. The immune system produces antibodies designed to fight specific invaders.
The antibodies start moving through the blood stream about a week after exposure to the virus.
Antibody tests, some of which are fingerprick tests read on the spot, and some of which require drawing blood from a vein and must be sent to a lab, are important for additional reasons:
- They can help scientists estimate the timing of infection.
- They can show how widely the virus infected the overall population.
- They can show how many front-line health care workers were infected.
- They are inexpensive compared to the molecular tests and can be manufactured by the thousands.
- They can provide an indication of the percentage of those who came down with COVID-19 had no symptoms and could have been “silent spreaders,” transmitting the virus without knowing it. (The U.S. Navy and the Centers for Disease Control & Prevention are investigating an outbreak on the aircraft carrier Theodore Roosevelt, where about 600 sailors were infected. Defense Secretary Mark Esper told the "Today" show that about 350 of those infected sailors were asymptomatic, meaning the virus can be carried "by normal healthy people.")
- They can identify people who can donate blood for experimental treatment of coronavirus sufferers. Scientists are studying whether transfusing plasma rich in antibodies into those patients can strengthen their immune systems against the virus.
There has not yet been definitive proof that people with COVID-19 antibodies are immune from reinfection, and if they are for how long.
Cuomo cited immunity as one reason for the state’s aggressive testing push.
Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, on Friday acknowledged that the extent and length of protection provided by antibodies has yet to be established definitively.
Still, he said that previous viruses provide some guidance.
“We are assuming that if you’re infected and you have antibodies, you’re protected,” he said. “That’s a reasonable assumption based on our experience with other viruses.”
Questions also have been raised by the accuracy of antibody tests.
Dr. Deborah L. Birx, coronavirus coordinator of the Trump administration’s coronavirus task force, on Friday said that health officials are seeing high antibody levels in many “individuals who don’t remember having an illness.”
Birx warned that some countries have found that certain antibody tests were “50%, 60%, 70% faulty” when deployed in the field.
The test being deployed in New York, created by the state’s Wadsworth Center Lab in Albany, was approved by the Food and Drug Administration, Cuomo said.
The antibodies, specific to the coronavirus, remain in the blood of those infected with COVID-19 for weeks afterward, regardless of whether a person had symptoms.
Finding high antibody counts through a blood test in a person with no symptoms indicates that a patient has recovered from the COVID-19 virus and is unlikely to transmit the disease.
But the extent and duration of any immunity remains in question. Some viruses, like the one that causes chickenpox, can confer strong immunity lasting many years. Others, such as HIV, may offer little or no protection.
On Friday, South Korea’s Centers for Disease Control & Prevention reported that 163 patients — 2.1% of the 7,829 patients who were in isolation — had tested positive again after being discharged. Whether that was because of faulty testing, an isolated pocket of virus that had not been cleared or actual reinfection, was under investigation.
Dr. Michael J. Ryan, executive director of the WHO’s emergencies program, said in a Friday news conference that “nobody is sure if someone with the antibodies is protected.”