Some uncertainties surround antibody tests The Mesa Tribune | The Hometown Newspaper for the city of Mesa, AZ

Some uncertainties surround antibody tests

Some uncertainties surround antibody tests

By Howard Fischer
Capitol Media Services

Amove 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 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.’’

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 UA test will be more accurate.

He added that the test is designed to make it “very unlikely’’ to return a false positive and is crafted to err on the side of telling someone who actually may have some antibodies that they do not, in fact, have protection.

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.

In the worst case, he said, “it’s probably not lasting for too much longer than a year,’’ he said. “A year ain’t too bad, though…From an epidemiological standpoint, if that’s what this confers, that’s not terrible.’’

All that presumes, Bhattacharya said, that the antibodies do 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.

“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.

But he stressed, “I would never be comfortable saying, ‘Well, you have an antibody test, go do whatever you want.’’’

But Bhattacharya said some of the accuracy issue comes down to how a test is 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.’’

He said tests run by central labs – like UA’s – 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.’’

“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.  γ

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