A blood test to determine who has been infected by SARS-CoV-2 is one thing, but a test to find out who has already had it is a whole different kettle of fish.
Because the coronavirus that causes COVID-19 can infect some people with absolutely no symptoms, an unknown number of people who are likely holed up in their homes have already been infected and are therefore immune. As the virus continues to sweep across the country, a test to find out who is immune will be key to re-opening the economy.
The Food and Drug Administration (FDA) has now authorized the first blood test, known as a serology test, to look for antibodies in the blood. Cellex Inc., a medical device company based in North Carolina, says the test could help physicians determine how widespread the virus is and the duration of immunity for people after they recover.
“Based on the totality of scientific evidence available to FDA, it is reasonable to believe that your product may be effective in diagnosing COVID-19,’ FDA chief scientist Denise Hinton wrote in a letter to James Li, CEO of Cellex. “The known and potential benefits of your product when used for diagnosing COVID-19 outweigh the known and potential risks of your product.”
“Current diagnostic tests, known as RT-PCR, are invasive and use genetic analysis to see if a person is actively infected,” Agence France Presse reported.
“Serologic testing, which only requires a drop of blood to conduct, focuses instead on finding virus antibodies, the presence of which indicates that an individual has had COVID-19 and is now likely immune. “Antibodies are one of the key immune response components. They start to be detectable around a week after initial infection,” said Andrew Preston, a reader in Microbial Pathogenesis at the University of Bath.
There are two types of antibodies associated with the COVID-19 immune response: IgM, which the body produces in the early stages of viral response, and IgG, which arrive later on during infection. The tests being developed can identify both antibodies, key hallmarks of a patient’s auto-immune response to the virus.
“Thus there is great interest in the use of an antibody test to indicate immunity against disease for use in the lifting of lockdown restrictions,” said Preston.
“In a vast majority of infectious diseases, recovery from disease and evidence of a strong immune response would lead to a period of immunity from re-occurrence,” he said.
Antibodies against the novel coronavirus are “generally detectable in blood several days after initial infection,” according to the FDA.
The Centers for Disease Control and Prevention also says it is working on its own serology test. Such tests are already in use for other illnesses and any new test for coronavirus antibodies can be analyzed in labs using existing hardware.
Once millions of people are tested, those who have antibodies can emerge from their homes and get back to work. “The main question is how to ensure everyone can return to work,” Francois Blanchecotte, president of the French Union of Biologists, told AFP.