What Is a Serosurvey? Blood of Americans Sought to Reveal the True Scale of the Nation's COVID-19 Epidemic

In the four months since the COVID-19 pandemic started, more than 1.4 million people have been diagnosed with the disease, according to Johns Hopkins University. But that figure includes only those who have been tested for the new coronavirus. What are known as serosurveys could help experts gain an understanding of how widely the new coronavirus which causes COVID-19 has truly spread.

A serosurvey is where the blood of a group of people is tested to see if they are carrying antibodies against a specific infection—such as the COVID-19-causing coronavirus named SARS-CoV-2 (not to be confused with the SARS virus). The immune system creates antibodies in order to remove invaders, like a virus. Therefore, the presence of antibodies can indicate whether an individual has previously been infected by and tried to fight off an infection.

Dr. Maria Van Kerkhove, infectious disease epidemiologist and COVID-19 Technical Lead at the World Health Organization (WHO), told Science the agency will in the next few days launch its Solidarity II program, which will see people's blood tested for SARS-CoV-2 antibodies in more than half a dozen countries. Speaking at a press conference two weeks ago, she said at least at least four studies were ongoing in different countries involving specimens already collected, which may include people hospitalized for other reasons, she said.

Van Kerkhove said, "This is critical for us to really understand what level of circulation this virus may have or may have had in people that may have had a subclinical infection so infection that has mild disease and maybe they didn't seek care or they weren't picked up through the current surveillance systems."

According to Science, by potentially revealing how many people have experienced a mild case of COVID-19 and are likely immune to re-infection, the tests could help policymakers decide when and how to ease lockdowns and quarantines.

In a statement on Tuesday, the U.S. Food and Drug Administration commissioner Dr. Stephen Hahn chimed that "serological tests can play a critical role in the fight against COVID-19 by helping healthcare professionals to identify individuals who have overcome an infection in the past and have developed an immune response."

Hahn said such tests could "potentially" be used alongside other clinical data to see if a person is no longer at risk of being infected and can return to work. They could also help doctors find those who can donate part of their blood plasma for an experimental treatment for those "seriously ill" with COVID-19.

However, Hahn said that as antibodies may not be detectable in the first few days a person is infected, such tests "should not be used as the sole basis to diagnose COVID-19."

"In March, the FDA issued a policy to allow developers of certain serological tests to begin to market or use their tests once they have performed the appropriate evaluation to determine that their tests are accurate and reliable," Hahn said. So far, 70 developers have notified the agency their tests are available for use, but Hahn warned some are falsely claiming their methods are FDA approved or can diagnose COVID-19.

Michael Busch, professor of laboratory medicine and a transfusion specialist based at the University of California, San Francisco, told Science his team is developing three large serosurvey studies in the U.S. "to detect ongoing incidence, to determine if antibody responses are waning, and to assess herd immunity." It is to the largest serosurvey currently planned in the U.S., he said.

The first part involves six metropolitan regions in the U.S.: New York City, the San Francisco Bay area, Los Angeles, Boston, and Minneapolis, according to Busch, who directs the non-profit Vitalant Research Institute which is associated with 170 U.S. blood donation centers. In addition, workers at regional blood centers are setting aside 6,000 samples for donors for the next five months, which with their associated data on variables like age, gender, and zip code should reveal which populations have antibodies. This would enable experts to compare information on regions and states.

The third part will see the team collaborating with researchers performing other population surveys, including at UCSF and the University of Washington, to pool their findings, he said.

Experts at Stanford University and Germany's University of Bonn are also hunting down antibodies in blood samples, according to Science.

Kerkhove told Science: "The fact that we're talking about all these studies just three months [after the disease was first recognized] is incredible.

But she stressed: "We want to latch on to any information that comes out," adding: "But we do need to interpret these initial results with caution."

Some countries, including Germany and the U.K., have floated the idea of issuing immunity certificates to those who test positive for SARS-CoV-2 antibodies. However, Dr. Peter Drobac, a physician and specialist in infectious diseases and public health at the Saïd Business School at the University of Oxford, told Newsweek: "We don't actually know much about immunity to the novel coronavirus yet, but early signs suggest that people who have recovered from COVID-19 are unlikely to be reinfected, at least in the short term.

"So knowing who has been infected can help determine who might safely go back to work or re-enter society, so to speak."

However, he argued the idea of "immunity certificate" or "immunity passport" are "dangerous." That's because it's not clear whether a positive antibody test means a person is immune, or for how long. "Nobody gets an immunity certificate for getting a measles vaccine, they get a vaccination certificate. So perhaps we should be calling these 'antibody certificates'," he suggested.

While they make sense for health professionals and oher critical workers, risks need to be addressed before they are issued to the general public, said Drobac.

"Imagine two employees of the same business, and one is allowed to come back because she has a certificate while the other has to remain out of work. Might you see people desperate to get back to work actively trying to get infected? Absolutely. Might you see people try to defraud the system to get a certificate even if they're still vulnerable to infection? Absolutely.

"There could be real unintended consequences here, it's an issue that needs to be addressed," Drobac said.