A wealth of new COVID-19 tests could soon help states more broadly track people in schools, dense workplaces and vulnerable populations.
In October, the supply of rapid-result COVID-19 tests, also known as antigen tests, shot up to more than 150 million — six times the number of tests of any kind performed in August and 10 million more than the total number performed in the United States since the pandemic began, according to the COVID Tracking Project, a volunteer-run organization begun by The Atlantic.
And unlike laboratory-based polymerase chain reaction tests, known as PCR tests, whose numbers can be expanded only in small increments, antigen tests can be produced quickly and cheaply to meet demand.
In theory, the growing supply of rapid-result antigen tests should allow millions of asymptomatic people — who make up at least 40% of those infected with the coronavirus — to be regularly screened for the virus, and for those who test positive to be isolated to curtail spread in classrooms, workplaces and other environments.
But so far, that’s not the plan.
Instead, most states say they expect to use the 15-minute tests to diagnose symptomatic people in prisons, police and fire departments, health clinics and other places that already are set up to conduct testing. Some states also are making the kits available to school nurses to test anyone who complains of symptoms.
A few states plan to use the new tests to control viral spread in specific high-risk populations. Alaska, for example, is sending tests to oil-drilling sites, while Mississippi and other states are shipping them to veterans homes, according to the U.S. Department of Health and Human Services. Nevada is sending them to tribal health clinics, and Colorado plans to use them to test homeless populations.
Public health experts caution against relying too heavily on rapid tests to defeat the pandemic.
“No test is perfect,” said Gigi Gronvall, an immunologist and senior scholar at the John Hopkins Center for Health Security.
“Without a plan, without a strategy, more testing isn’t going to get us out of this pandemic,” Gronvall said. “Anybody who thought testing was the way out just has to look at the White House to see that if you rely on testing alone, you’re going to fail.”
At a Sept. 26 Rose Garden event to introduce Supreme Court nominee Amy Coney Barrett, more than 200 mostly unmasked attendees sat close to one another, shook hands and hugged in part because frequent antigen testing led them to think they were safe, Gronvall explained. Following the event, President Donald Trump and his wife, Melania, tested positive for the virus, as well as at least nine attendees, as part of an outbreak of more than two dozen cases connected to the White House.
Mask wearing, physical distancing, limiting the size of gatherings and holding them outside, along with hand washing, building ventilation and other measures will still have to be maintained, even if every person in the country gets tested every day, Gronvall said.
In addition, health experts point out that even the most accurate COVID-19 test is only a snapshot in time. People infected with the novel coronavirus can test negative before the virus reaches a level that can be detected and be contagious days or hours later. Alternatively, people can get a negative COVID-19 test result in the afternoon and become infected that evening.
The federal government shipped 100 million credit card-sized rapid-result antigen tests to states in October, leaving it up to governors to decide how to use them. Made by Abbott and branded BinaxNOW, the tests cost $5 and can deliver results in 15 minutes to patients’ cell phones.
The government also sent another 50 million kits to nursing homes and other residential care settings, Indian Health Service clinics and historically Black colleges. The federal purchase depleted Abbott’s entire inventory, but the company has said it will produce 50 million more tests per month.
But despite the exponential rise in COVID-19 testing capacity, some leading public health experts argue the United States still doesn’t have enough.
Harvard epidemiologist Dr. Michael Mina estimates that with 330 million people, the nation needs tens of millions of tests per day if schools and businesses are going to stay open without causing a surge in the virus.
Screening and Surveillance
Many health experts recommend the growing supply of antigen tests be used for screening and surveillance, leaving more accurate laboratory-based tests for diagnostic use in hospitals and other health care settings.
Screening for COVID-19 involves testing everyone in a school, workplace or community at regular intervals to detect infections in asymptomatic people so they can be isolated. Screening can also be used to check everyone attending an event or, for example, getting on a plane.
Surveillance, meanwhile, involves randomly testing asymptomatic people anonymously to gauge the prevalence of the virus in a community, school or workplace. In some cases, surveillance is conducted by pooling randomly collected test samples or testing wastewater.
If surveillance indicates that the prevalence of the virus is rising in a particular population, more frequent screening may be implemented.
In both screening and surveillance, anyone who tests positive using a rapid-response antigen test is asked to quarantine and take a more accurate PCR test to confirm the infection. With pooling and wastewater testing, everyone is asked to take a test if the virus is detected in the sample.
Antigen tests have received emergency use authorization from the U.S. Food and Drug Administration only for use on symptomatic people. Nevertheless, health experts widely recommend their off-label use for screening asymptomatic people.
Some epidemiologists and infectious disease experts argue that the tradeoff between the accuracy of the PCR tests and the speed, availability and low cost of the antigen tests makes the latter more valuable for screening. Mina and others argue that frequent retesting will result in detection of most false negatives.
Since the pandemic began, PCR tests, which require analysis in a specialized laboratory, have been the primary tool for diagnosing coronavirus infections. Considered the gold standard, they are nearly 100% effective at identifying the presence of the virus’ genetic code or RNA.
Antigen tests tend to be 97% to 98% effective at identifying proteins associated with the virus. But clinical trials for the test were only conducted on people exhibiting COVID-19 symptoms. When used on asymptomatic people, the tests’ accuracy may be lower.
Both antigen tests and PCR tests are currently being used for screening in some universities, health care settings and businesses. But widespread screening has not yet taken off.
That’s not likely to happen until January, according to Mara Aspinall, professor of biomedical diagnostics at Arizona State University.
“When the second semester rolls around and businesses want to bring back workers after the holidays, that’s when we’re likely to see much more use of antigen tests for screening,” she said.
In the meantime, even if the current COVID-19 surge gets much worse, Aspinall said, the supply of PCR tests is likely to hold up. As antigen tests become more available, she said, they will be substituted for PCR tests in screening and surveillance programs to preserve the supply of PCR tests.
Liability and Supply
The lower accuracy rate of antigen tests has given pause to some state officials and school administrators when considering whether to use them in vulnerable nursing home and K-12 school settings, said Eileen O’Connor, senior vice president of communications, policy and advocacy at the Rockefeller Foundation, which is working with states to develop strategies for COVID-19 testing.
“Some fearful state officials want the FDA to issue full approval of antigen tests for asymptomatic people before they commit to any major screening programs,” she said. States, school administrators, nursing home operators and others also want to see national protocols for COVID-19 screening using antigen tests, she said.
In late October, the federal Centers for Disease Control and Prevention issued recommendations for school administrators on how to use antigen and PCR tests for screening and surveillance. In addition, the Rockefeller Foundation published a report on testing in K-12 schools as a way to safely bring kids back into classrooms.
But there’s another reason that states haven’t yet committed to broad screening programs in schools and other high-risk settings.
“States don’t want to go down the road of promising schools they can have the tests they need for screening and then not be able to provide them because the price is too high or the supply doesn’t last,” said Dr. Marcus Plescia, chief medical officer for the Association of State and Territorial Health Directors.
If all 50 states were to commit to testing the nation’s 50 million K-12 students, those 100 million tests would be used up quickly, he said. Some states have formed a purchasing compact to secure future supplies of the tests, Plescia said, but they need more assurance that manufacturers will be able to produce them at a price they can afford.