PHOENIX — A move by the University of Arizona to test 250,000 Arizonans for COVID-19 antibodies comes as scientists are still debating how much protection against future infection a positive result means — and, more to the point, for how long.
“The first infections came out in December,’’ said Deepta Bhattacharya, an associate professor at the Department of Immunobiology at the school’s college of medicine. “And so we really don’t have any way to know ahead of time how long immunity’s going to last.’’
And Bhattacharya acknowledged a recent study finding that a majority of tests now on the market have accuracy rates that make them effectively useless.
But he said that the test that UA is rolling out will be more accurate in determining if there are antibodies present than some of what’s on the market now.
And if nothing else, he said the test is designed to make it “very unlikely’’ to return a false positive. In fact, Bhattacharya said, it is crafted to err on the side of telling someone who actually may have some antibodies that they do not, in fact, have protections.
“We decided that was probably the lesser of two evils given that we don’t want to give people a false sense of security,’’ he said.
All that, however, comes back to the question of what does the presence of COVID-19 antibodies actually mean.
Bhattacharya said the whole belief that these provide some level of immunity is based on what he called the “garden-variety coronaviruses’’ which have been around and where there are studies. That includes things like MERS — Middle East respiratory syndrome — and severe acute respiratory syndrome, or SARS.
In the worst case, he said, “it’s probably not lasting for too much longer than a year,’’ he said.
Still, Bhattacharya said, that’s nothing to sneeze at.
“A year ain’t too bad, though, I guess is what I would say,’’ he said. “From an epidemiological standpoint, if that’s what this confers, that’s not terrible.’’
All that presumes, Bhattacharya said, that the antibodies do, in fact, confer some immunity.
He pointed out that the World Health Organization earlier this month said there was no evidence that antibodies prevent reinfection.
“And then I think they heard from many irritated scientists such as myself saying, ‘What do you mean by no evidence?’ ‘‘ Bhattacharya said. He said it might have been more accurate for WHO to say that they “need more evidence.’’
WHO later backed down, Bhattacharya said, modifying their statement to say that most people will generate antibodies when they get infected, and that those antibodies are “expected to generate some degree of protection.’’
“Now that’s vague,’’ he acknowledged. “But that’s essentially the data on the ground.’’
A lot of the research, Bhattacharya said, is occurring with scientists extracting the plasma from people who have recovered from COVID-19 and giving it to people in intensive-care units who are having trouble controlling the virus.
He said the number of such tests are limited, meaning the sample size may not be enough to draw any major conclusions.
“But at least in those small studies it seems like that actually has quite a bit of benefit,’’ Bhattacharya said. He also said there have been some non-human studies in primates like macaques where they’ve infected the animals intentionally and then been unable to reinfect them later.
And Bhattacharya said he and other scientists have done experiments with antibodies and cell cultures.
“And what we’re seeing is that people who have antibodies have at least some degree of neutralizing the virus, meaning preventing it from getting into cells,’’ he said.
All of those things, Bhattacharya said, comes with a certain degree of uncertainty.
“I would never be comfortable saying, ‘Well, you have an antibody test, go do whatever you want,’ ‘‘ he said. But Bhattacharya said everything he has seen so far leads him to believe that “some degree of immunity is conferred.’’
That, however, raises the other question: How accurate are the tests?
Bhattacharya noted research funded by the Chan Zuckerberg Biohub found that some of the tests now on the market have an accuracy rate of less than 90%.
“That was highly concerning.’’ he said.
But Bhattacharya said some of that comes down to the type of test being administered.
“One of them are called these point-of-care or ‘finger-prick’ antibody test,’’ he said. The advantage of those, he said, is it involves just a small amount of blood and that yes-or-no results can come back within an hour.
“From a logistical standpoint and getting many people tested, there’s a lot of upside to having a test like that,’’ Bhattacharya said. But as the research found, “a majority of them are really quite bad.’’
Consider, he said, a test with a 98% accuracy rate, meaning that 2% are false positives.
“Now, that sounds better than it is,’’ Bhattacharya said. “When you have a state where there’s only 2 percent true positives, then one out of every two tests returned is going to be wrong.’’
And, he said, it’s complicated by people analyzing the results which he said can be like reading a home pregnancy kit.
By contrast, he said, tests run by central labs — like the kind UA will be doing — are more accurate. But they have their own drawbacks.
“That requires a blood draw,’ Bhattacharya said. “And so there are some logistical issues with that in testing large numbers of people.’’
Still, he said, it produces an actual number that is related to the antibodies, not a color code on a stick.
“You’re not relying on the human eye,’’ Bhattacharya said. And that, in turn, allows scientists to set “very strict cutoffs’’ for telling people whether they have a positive antibody test.
“What that means, also, is we err on the side of false negatives, meaning someone who may have some low levels of antibodies, our tests might call them negative. And that, he said, comes back to the decision on “the lesser of two evils’’ to not give people that false sense of security.