It's one of the most pressing Coronavirus questions: If you survived COVID-19, does that mean you cannot get it again?
In other words, do the response antibodies in your bloodstream give you immunity?
The hope is they do — that the growing bumper crop of test kits for COVID-19 antibodies can do more than just tell us who has already had COVID, but more importantly, who is safe to be exposed to the disease if they are indeed now shielded from it.
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But officials continue to stress that they don't yet have the data to be sure.
Using antibodies to determine if you are not infected now, but were earlier, is something that cannot be done by the main COVID test, the so-called "PCR" or "molecular" test. That test usually involves a swab to sample your mouth or top of your throat for evidence of the virus. It reveals whether you currently are infected.
Enter the blood serology test, which evaluates a drop of blood drawn with a pinprick of your finger, to determine if you have developed antibodies.
Attempting to pick and prick, adults at random and surveying 863 of them, a study earlier this month by USC and Los Angeles County Public Health found that 4.1% had antibodies and therefore must have had COVID at one point.
Multiplying that rate by the about 8 million adults in the county provides an estimate that perhaps 320,000 Angelenos have had COVID — far more than the 20,000 confirmed infected by the molecular test.
With multiple manufacturers, many in China, producing COVID antibody tests, many private medical practices have obtained them and are testing requesting patients who believe they may have been exposed.
"I definitely do believe that this is going to be the next stage in overcoming this virus and, you know, getting back to our routine lives," said David Nazarian, MD, a physician in Beverly Hills who calls his practice, My Concierge MD.
Dr. Nazarian is offering the test by appointment for $225, including consultation, he said.
One who took the test last week, Scott McIntosh, said he wants to know if it was Covid-19 that caused him to get so sick in February.
"This can be a really great way to get to the next level," McIntosh said.
Dr. Nazarian believes it likely the presence of antibodies gives a measure of protection, and notes that injections of antibody rich plasma from recovered COVID patients are being used increasingly to treat severe cases.
But he acknowledges the level of immunity afforded to recovered patients has not been confirmed or quantified.
"We don't want the public to interpret these test results as, 'Oh I think I have immunity' because that question hasn't been credibly scientifically answered yet," said Neeraj Soon, a professor at the USC Price School of Public Policy and a principal investigator with the antibody survey in LA County.
Some private practices offering the antibody test are asking patients to sign a waiver, acknowledging a positive test does not mean they cannot catch, or infect others with COVID-19.
And yet, clearly there's an expectation in the biomedical community that COVID antibodies do provide at least some protection, and that studies underway will prove it. Gov. Gavin Newsom announced last week that California has come to an agreement with Abbott Laboratories for 1.1 million serology test kits.
"As we are more confident that the antibodies that we're testing for actually neutralize--if they do--neutralize the virus, to be able to say somebody has been exposed and they are protected to a certain degree. But I caution you that we are not there yet," said Dr. Mark Ghaly, California's secretary of Health and Human Services.
So, for now, what can physicians tell their patients who test positive for antibodies?
"Good question. I'm telling them that, for now, it looks like they have developed immunity," said Dr. Nazarian. "Our bodies are producing antibodies and they are overcoming this virus. I think the controversy is how long do these antibodies last, how effective are they? But if you look at, for example, this convalescent plasma therapy that they're doing for patients that are actively ill, you see that it works, it helps. So there's definitely a response."
The FDA allowed the new serology tests on an emergency basis. There's consensus not all are created equally accurate, and even the best may indicate some false positives or false negative. LA County's public health director said the test they used with USC--also one of the tests Dr. Nazarian uses--sometimes misses antibodies, that 20% of the time the result comes back negative, antibodies might actually be present.
Some nations are already exploring prospects for using antibody results as the basis for so-called "immunity passports" that would give the bearer greater freedom of movement during social distancing. But that is premature, cautioned Catherine Smallwood, senior emergency officer at the World Health Organization Europe.
"Hopefully I'm immune, whatever that means for the time being," said McIntosh the day he took his test. "But you know what? I'll take it."
With its big order, California is betting antibody testing will be usable for more than just determining who once had COVID.
"And as soon as we are confident in how to use that modality in California, we will communicate that clearly and assertively," Dr. Gahly said last week.
Among the lingering concerns is that immunity can lessen over time, as the virus mutates or for other reasons. Consider one famous coronavirus that most of us get over and over again during our lives: the common cold. It's hoped in that sense COVID-19 is different from its far less lethal cousin.