While antibody tests are broadly seen as a way to determine immunity and exposure to the pandemic coronavirus, the Food and Drug Administration (FDA) recently warned that tests should not be used as the “sole basis to diagnose COVID-19.”1

“The FDA is not aware of an antibody test that has been validated for diagnosis of SARS-CoV-2 infection,” the agency wrote in a letter to healthcare providers. “While the FDA remains open to receiving submissions for these tests for such uses, based on the underlying scientific principles of antibody tests, the FDA does not expect that an antibody test can be shown to definitively diagnose or exclude SARS-CoV-2 infection.”

The FDA recommendations for healthcare providers include:

  • Continuing to use antibody tests, as appropriate, while aware of their limitations;
  • Using antibody tests as information about whether a person may have been exposed, rather than as a diagnostic tool;
  • Being aware that not all marketed serological tests have been evaluated by the FDA. FDA-authorized tests are listed on the Emergency Use Authorization (EUA) page.2 Tests offered under a policy outlined in the FDA’s COVID-19 Diagnostic Policy Guidance are listed on the FDA’s frequently asked questions page. Such tests have not been reviewed by the FDA, unless an EUA has also been submitted and reviewed by FDA.

While antibody testing is a work in progress, it has the potential to answer questions key to fighting the pandemic. One of them is whether those who survive infection with SARS-CoV-2 generate sufficient antibodies to be immune for some time.

“That is certainly the hope,” says William Schaffner, MD, an infectious disease physician and professor of preventive medicine at Vanderbilt University. “If you look at the human coronaviruses — the ones that cause the common colds — you do get strain immunity, but it begins to wane fairly quickly after about a year. But that kind of immunity would be terribly important in blunting a resurgence of this virus in the fall. It might be a bridge to the time we can get a vaccine deployed.”

Anthony Fauci, MD, director of the National Institutes of Health’s National Institute of Allergy and Infectious Diseases, also recently commented on this issue in an interview.

“Right now, we don’t think that this [SARS-CoV-2] is mutating to the point of being very different,” Fauci said. “We are making a reasonable assumption that this virus is not changing very much. If you get infected in February or March — and then recover — then next September or October, I believe that person is going to be protected. We are not 100% sure. But I think that is a reasonable assumption.”

However, Fauci took a cautious tone regarding the antibody tests now coming on the market. The tests certainly have great promise to affect the coronavirus response, but the antibody diagnostics must be carefully validated before they are widely distributed, he emphasized.

“There have been international incidents where a country has ordered millions of these tests from another country, only to find that they don’t work,” he said. “We have to validate these tests — that’s absolutely critical. Otherwise, you will go down a path that will be very misleading.”

REFERENCES

  1. Food and Drug Administration. Important information on the use of serological (antibody) tests for COVID-19 — letter to health care providers. April 17, 2020. https://www.fda.gov/medical-devices/letters-health-care-providers/important-information-use-serological-antibody-tests-covid-19-letter-health-care-providers
  2. Food and Drug Administration. Emergency Use Authorizations. Industry hotline: Coronavirus COVID-19 diagnostic tests and shortages. https://www.fda.gov/medical-devices/emergency-situations-medical-devices/emergency-use-authorizations