Just one half of one percent of Americans have undergone the invasive and nearly impossible-to-get test for COVID-19, according to the Surgeon General, so a simple blood test to determine who’s had the disease and is presumably immune sounds like a game-changer.
But like everything else about the disease, uncertainty reigns.
A test from Cellex that measures antibodies, the cells produced by the body to fight the coronavirus, received approval for emergency use last week by the U.S. Food and Drug Administration.
Antibody testing is crucial to learning the extent of the disease’s spread, developing vaccines, possible therapies for treating the sick, and in determining who should return to work — especially first responders and health care workers.
“It’s the way we really defined the HIV epidemic in the United States,” Dr. Deborah Birx, the response coordinator for the White House coronavirus task force, said at the task force’s April 1 briefing. “We were able to go back to blood samples when we had the test and really find out where it was and what was going on.”
“We really need to look in here and really see: Was there virus significantly circulating in early March and late February? And what did it look like? And where was it? And was it all in the metro areas?” Birx asked.
While some are eager to deploy the tests, other experts fear testing at the wrong time could do more harm than good.
“Right now, that’s not our immediate problem,” Dr. Anthony Fauci, director of the National Institutes for Allergy and Health said at a White House Task Force briefing Wednesday.
Fauci said the HIV antibody test developed in 1985 told experts “that we were dealing with the tip of the iceberg” when it came to known infections.
“It gave us a really good feel for how many people were infected, how many are doing well, and how many are getting ill,” Fauci said. “I foresee that we’ll have that same sort of information, which will be important information, but right now that’s not our immediate problem.”
“They have to be used carefully. Used too early, the convalescent patient may still be carrying and shedding the virus, they may still be a risk to others,” said Michael Skinner, a reader in Virology at Imperial College London told Philippine news service ABS.
“Antibody testing is not a priority at this time for us,” says Dr. Mark Pandori, director of the Nevada State Public Health Laboratory. “The information provided by such tests is not necessarily actionable for many reasons at this stage of the scenario.”
Pandori says there’s a sweet spot in which antibody testing is most valuable.
“Antibody is generated in response to an infection. First, within about three weeks, a person makes an antibody class called IgM. Then after another one to two weeks, they make a second antibody class called IgG,” Pandori explained.
He says those tested “within the first three weeks of infection would be negative” for both antibodies. “So a person could very reasonably be infected but come up negative on a test.”
A positive antibody test could mean a person was exposed and possibly never had symptoms, says Pandori, or they are currently infected, which he says is less likely “given that a person is only infected for a couple of weeks.”
“So, as you can see, neither result on an antibody test is that meaningful. The PCR test we use tells you: is someone infected, right now? That helps a lot more,” he says.
Pandori says antibody testing for COVID-19 will be meaningful “after all this settles down, testing people en masse” to determine how many were infected and how many were asymptomatic.
The United Kingdom intends to institute widespread antibody testing and issue “immunity passports,” which would give holders early exit from lockdowns, according to news reports.
Doesn’t antibody testing make it easier to identify first responders and health care workers eager to return to the front lines?
“No, in fact, it makes it harder, I think,” says Pandori. “If you test those people and they are negative, what does that mean? It doesn’t mean you’re not infected. You could have been infected in the last three weeks and you would be negative on that test. Now that is really bad because you would be giving dangerous false information to someone who is about to become a virus spreading machine.”
“We learned all this with HIV in the late 80s and 90s. Antibody tests given too early, are not good,” Pandori says. “A PCR test on the other hand, now that tells you what you need to know: can we see virus in your body? Are you secreting virus? PCR is very sensitive that way.”
But PCR testing, which samples nasal and throat swabs at this point, is a relatively laborious process compared to antibody testing, which requires a tube of blood, or in a more advanced stage of development, just a drop.
Dr. Brian Labus, an assistant professor at UNLV and a member of Gov. Steve Sisolak’s COVID-19 medical advisory team, sees no reason to hold off on antibody testing.
“Those tests will tell us how much asymptomatic and undiagnosed disease has occurred, so there is no reason to wait,” Labus says, adding he’s not aware of when the tests will be available in Nevada.
“It takes at least a few days for your body to produce those antibodies, so testing should be performed later in the disease,” he says. “IgM Antibodies usually last about 6 months. IgG antibodies are the ones that provide long-term immunity and would be created after immunization, if we are able to create a vaccine. You can detect those for much longer, assuming that we don’t have a loss of immunity over time. We do not know if that is the case or not.”
That unknown complicates efforts to return workers presumably immune to reinfection to hospitals, fire departments, child care centers, grocery stores and other places people could be infected.
“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,” Andrew Preston, an expert in Microbial Pathogenesis at the University of Bath told AFP, a global news service. “(But) the caveat is that we don’t know for sure that a positive antibody test does imply someone is immune (from COVID-19).”
Advocates of widespread antibody testing point to the potential for using the plasma of recovered patients to treat those currently infected. A Japanese company is working to develop such a process.
“This is an old concept,” Fauci said at a White House briefing. “In fact, immunology was born decades and decades and decades ago with the concept of giving passive transfer of serum to an individual to protect them from an infection.”
The U.S. Department of Health and Human Services recently awarded $14.5 million to Emergent BioSolutions, which is working on two therapies using plasma from recovered patients.
A successful protocol would land recovered patients who donate plasma in yet another category of unlikely heroes in a war that has put grocery clerks, child care workers, and delivery drivers on the front lines.