Seven months into the pandemic, the U.S. needs to rethink its approach to testing for COVID-19, experts say, by shifting to cheaper tests that can return results in less than an hour, potentially finding people when they are most infectious and containing outbreaks before they explode.
The Food and Drug Administration (FDA), however, appears reluctant to approve those tests for sale in the U.S. because they are typically less accurate or unable to detect small amounts of virus compared to the gold standard, high-sensitivity lab tests the U.S. has been relying on.
As demand for tests surges, those lab tests have taken longer and longer to return results, making it extremely difficult to contain outbreaks.
The rapid tests, some of which can be used at home, aren’t the gold standard and can miss infections but experts say they make up for it through their speed and low cost. Because they're cheaper, they could be made available to millions of people to use several times a month, experts say.
Additionally, the tests are actually very good at detecting virus when it matters most: at high or peak levels, when an individual is most contagious to others, experts say.
“If you want to be certain about whether somebody is infected or not these tests are not so great. If you want to identify whether they're infectious or not going to go out and spread to other people, these tests are actually quite good,” said Ashish Jha, a physician and director of the Harvard Global Health Institute.
The United States ran about 5 million tests the last week of July, a significant improvement from the early days of the pandemic when tests were hard to come by. Commercial labs now run about half of the COVID-19 tests across the country. But turnaround times have grown longer as demand surges for testing in states in the South and West, where outbreaks are leading to thousands of new COVID-19 cases per day.
Demand for tests is expected to grow in the fall, when students return to school and the flu season hits.
Experts say rapid tests would allow individuals to regularly screen themselves for COVID-19 before they go to work, school, or other areas where they could potentially spread the virus to others.
Harvard’s Michael Mina envisions a $1 antigen paper strip test — similar to pregnancy tests — that could be manufactured by the government and distributed to millions of people to regularly screen themselves.
Several companies are working on similar tests now, but have been slow to ask for FDA approval because it doesn’t meet the agency’s standard for high sensitivity.
“Our goal is to make an at-home test, but because of FDA criteria, we believe there’s a longer path to get there,” said Carlos-Henri Ferré, spokesman for E25Bio Inc., a company that has its roots in developing rapid tests for mosquito-borne illnesses.
Within the next few weeks, E25Bio plans to ask the FDA to approve a rapid antigen test that will initially only be available in clinical settings because that is what the FDA will approve.
But eventually, the company hopes to have a home-based test that could be easily used and accessible to anyone.
“I think FDA is not quite there yet. I think that they could come around to it, but I think there will be a lot of steps required to get to a place where we can have an at-home antigen test,” Ferré said.
While the at-home rapid tests are less sensitive than the lab tests, Ferré said they could be of critical help to the United States.
“A test like ours is very effective in detecting high viral loads, meaning people like super spreaders,” Ferré said. “We think this is a very effective screening tool to separate infected individuals who have the highest chance of spreading virus and continuing the outbreak versus people who don’t.”
Experts say rapid antigen tests should ideally be used multiple times a week, especially for essential workers and others who have a higher risk for exposure.
A negative result doesn’t necessarily mean someone doesn’t have COVID-19. It could also mean they have lower levels of the virus that the test can’t detect yet.
“We have to stop thinking about this as somebody gets a negative test they get a clean bill of health, they can do whatever they want," Jha said.
"That's not what the point of these tests are. The point of these tests is we're doing them frequently, you're getting results frequently. And if you tell somebody who has a negative test, 'you're not infectious today, but you could be infectious tomorrow, you still need to wear a mask, you still need to do social distancing, and we’re going to retest you in three days' — if we have that strategy for high-risk people, we really can make a big difference.”
Only 1 out of 10 COVID-19 infections are being detected through testing, according to a recent CDC estimate.
That is partly because a high percentage of infections — up to 45 percent — are thought to be asymptomatic, meaning they harbor the virus, and can transfer it to others, but won’t experience symptoms themselves.
Regular screening using rapid tests will do a better job of finding people who have COVID-19 but aren’t showing symptoms, experts say.
Without regular screening, an asymptomatic person might not even have reason to get a test, and could potentially spread it to more vulnerable people who could experience serious illness or even die.
A study led by Daniel Larremore at the University of Colorado, and several other colleagues, modeled the benefits of frequent testing in a paper that is not yet peer-reviewed and found frequency and speed of testing outweighs high sensitivity.
“The purpose of a screening test is to identify as many infections as quickly as possible,” Larremore said.
If moving to a less sensitive test “means we can do 10 times as many tests, from the screening point of view, that’s a great trade-off to make” because you’ll catch more infections than if you tested fewer people using a higher sensitivity lab test, he said.
"The key thing rapid turnaround tests do is they give you highly sensitive results around the time you're most infectious to others," he added.
The FDA has approved two point of care tests, by Quidel Corporation and BD, that detects COVID-19 antigens. These tests can return results in 15 minutes and have a higher sensitivity than paper strip antigen tests but are more expensive and are not intended for home use. The tests require machines, most of which are in nursing homes and doctors' offices.
Governors of six states announced Tuesday they would band together to buy 300 million rapid antigen tests to be used with BD and Quidel machines to “better detect outbreaks more quickly” and expand long-term testing in congregate settings such as schools, workplaces and nursing homes.
The tests are about as accurate as the gold-standard lab tests but still aren’t widely available or accessible to the general public.
As far as paper antigen tests go, the Trump administration has indicated it sees a role for them, as long as they’re as accurate or sensitive as possible.
“The FDA standard is over 80 percent and I think with what we're seeing with the antigen tests, that is not too high of a bar to achieve because several have achieved it,” Adm. Brett Giroir, the administration’s testing czar, told reporters last week, referring to the BD and Quidel machines.
“There are several more that are very low cost that would be in that range that are being considered.”