Antibody tests, also called serology tests, look for the presence of antibodies in a person’s blood, which can show if someone was infected with the coronavirus in the past.

 Rebecca Sasnett / Arizona Daily Star

Early results from the University of Arizona’s highly publicized coronavirus antibody test show roughly 1% of local subjects had developed antibodies to help minimize the spread of the coronavirus.

That suggests Pima County and Arizona are still a “virgin territory for the virus,” according to Dr. Janko Nikolich-Zugich, a UA professor and head of the school’s department of immunobiology, whose labs are overseeing the tests.

“We have lived with it and have been in social isolation for a while … and the virus has really not spread much throughout Arizona,” he told the Star last week.

The UA has done 11,000 tests since the initiative was launched in April. Researchers analyzed the results from the first 5,845 subjects, which included health-care workers, members of the UA community, and those from the general public, all from Pima County.

Only 74 people — or about 1.3% — had antibodies, although that rate was slightly higher for health-care workers (just over 2%), lower for the general population (under 1%) and higher for the UA community (about 3%), although the last sample included only about 300 people.

Nikolich-Zugich said the results were below what researchers expected, but labeled it a “half-empty, half-full situation,” in that it shows public efforts, such as social distancing, did what they were intended to do in terms of slowing down the spread of the virus.

The caveat, he said, is it shows the public is nowhere close to developing herd immunity, or the levels of those with immunity to the virus, either through contraction or a vaccine, that are necessary to provide protection to those who are immune to the virus.

‘Widespread community transmission now’

Theresa Cullen, Pima County’s new health department director, said there are a number of things that could impact the accuracy of the results, including the limited sample, the time the test was taken and the test itself.

She pointed to the fact that “there’s widespread community transmission now,” referring to a recent spike in positive cases and hospitalizations, which could show a different result than those who were tested for antibodies over a month ago.

“The bottom line is we need an antibody test. We need to be clear what we’re using it for. We need to figure out what the rates in the population are of the disease, especially in younger people when we assume that they may be asymptomatic,” she said.

“What we’re really hoping for is to have some other metric that will allow us to measure the immunity that is occurring in the community. We know there’s widespread community transmission now. We’re seeing that in the increased number of cases. If asymptomatic, or minimally symptomatic, transmission is also occurring at an accelerated rate right now, that would help us predict when we think we will reach herd immunity.”

Will Humble, executive director for the Arizona Public Health Association and former state health director, said he’s “disappointed,” not that more people haven’t been infected, but rather that the state is no closer to developing herd immunity.

The state health department includes results of antibody tests on its website, although it’s unclear if that includes the results of the UA tests.

The positivity rate of the 128,381 tests across the country was 3%, as of Saturday.

Humble said it is not surprising that the number is higher than the UA tests because it represents those who scheduled an antibody test because they had reasonable suspicion they were exposed to the virus.

He said he expects the remaining results of the UA test will be about the same because they’re focusing on the same population.

Building antibodies to fight infection

Antibody tests, also called serology tests, look for the presence of antibodies in a person’s blood, which can show if someone was infected with the coronavirus in the past.

Antibodies are proteins that help fight off infections and usually prevent a person from developing the disease again, making them immune. Because the virus that causes COVID-19 is so new, however, it is not yet known how long that immunity will last or whether a person will be fully protected from future infection.

The performance of these tests is characterized by their sensitivity, or the ability of the test to correctly identify those who are positive for the virus, and by their specificity, or the ability of the test to correctly identify those who are negative.

The higher the sensitivity, the fewer false negatives a test will give. The higher the specificity, the fewer false positives.

Mark Lane, vice president of communications for UA Health Sciences, said the test developed by the university was determined to have a sensitivity rate of 95.6% and a specificity rate of 100%.

Like many antibody tests, the UA’s has not yet received FDA approval, although an Emergency Use Authorization request was filed with the FDA to allow testing to begin.

The UA says it anticipated approval of the tests “in the coming weeks.”

Even in tests with high rates of sensitivity and specificity, over 90%, the Centers for Disease Control and Prevention warns that in populations where the prevalence of the virus is low, less than 5%, it’s possible that less than half of those testing positive will truly have antibodies.

Nikolich-Zugich expressed confidence in the accuracy of the tests, saying the researchers conducted further testing and determined there were zero false positives.

“The test has definitely done its job and it’s not done doing it’s job,” he said.

“We are very confident that for the whole state of Arizona, we may return one false positive for 7 million people.”

Nikolich-Zugich said they will probably do the next analysis around 15,000 tests. He added their ultimate goal is to open it up to the general population, although there is no timeframe on when that will happen.

A well-publicized effort

In April, University of Arizona President Robert C. Robbins announced his intent to test 60,000 faculty and staff for the virus through the antibody tests. Shortly after, the state kicked in $3.5 million to test 250,000 health-care workers and first responders across the state.

Gov. Doug Ducey and Robbins have since highlighted the antibody test as one of the efforts the state is taking to trace the pandemic across the state.

Robbins has also used the program as a talking point during a media blitz on nationwide cable news networks and newspaper editorials.

It remains unclear how, if at all, the data from the test results is being used by the state to help determine reopening procedures.

In an interview with the Star, Dr. Cara Christ, the state’s health director, declined to comment, saying she hadn’t seen the early results herself.

Humble called the $3.5 million investment a “drop in the bucket” for the state considering the value the results provide.

In addition to herd immunity, he said the results show how health-care workers were able to practice safe care measures, even as they face well-documented problems like shortages of personal protective equipment.

“It shows how diligent and fastidious as a group they have been or the percent positive would be way higher,” he said.

In terms of using the data to make policy decisions, Nikolich-Zugich said his bigger concern is “we jumped into the reopening,” and that curbing the spread of the virus is “up to the sum of behavior of individual people.”

“The thing that makes me nervous is we’re still doing a lot of things by trial and error, where we should not be doing that,” he said. “There is so much information from what other countries did well, what we did well at times, and what we can learn. Still the reopening was not driven by a strategy of what we’re going to do.”

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Contact reporter Justin Sayers a jsayers1@tucson.com or 573-4192. Twitter: @_JustinSayers. Facebook: JustinSSayers.