Potential New Weapon Against Covid-19: Rapid ‘Crappy’ Tests
The FDA is reluctant to approve $1 home-based tests that could drive the pandemic down, experts say
Tests that determine if people have Covid-19 are not helping tamp down the pandemic, experts say. There’s just too much of the coronavirus circulating, too many infections, and those nose-invading PCR tests take forever to yield results, rendering them largely useless. Scientists who understand the problem don’t hold out much hope that the effort will get better anytime soon.
“Our current strategy is so woeful,” says Ashish Jha, MD, a practicing internist and professor of medicine at Harvard Medical School. “We’re not going to be able to improve our current testing strategy to a point where people will be able to get results quickly.”
In the United States, 700,000 nose-swab PCR tests are being performed daily, on average, up from around 500,000 two months ago. But most people don’t get results for at least two days, and turnaround times range up to two weeks, Jha says.
The testing system “is flailing, with raging outbreaks occurring,” says Michael Mina, MD, an assistant professor of epidemiology at Harvard T.H. Chan School of Public Health. “Maybe we only need a really crappy but fast test.”
“They are not so sensitive when you have a low amount of virus. But when you’re actually really infectious, you have large amounts of virus in your throat, elsewhere, and the test becomes much, much better.”
Less sensitive but more useful
The idea, which Jha says scientists have been discussing for some time, involves a paper strip and a tube of chemicals to quickly analyze saliva or snot. The concept was outlined by Mina and Boston University economics professor Laurence Kotlikoff in a July 3 New York Times opinion piece, and again by Mina in an August 3 Harvard Magazine article. (The at-home tests are distinct from saliva tests approved by the Food and Drug Administration this week, which still require analysis in a lab.)
Everyone should have these home tests, which might be as cheap as $1, Mina argues. They could be self-administered several times a week, returning results in about 15 minutes. It’s already possible: Several academic labs and at least three companies — E25Bio, Sherlock Biosciences, and Mammoth Biosciences — are working on such tests and some have already submitted the products for federal approval.
But the FDA has been reluctant to approve them because of their lower level of sensitivity compared to PCR tests, Mina says.
The cheap, rapid tests are admittedly less than perfect, everyone agrees, but that does not make them bad.
“They’re not actually crappy tests,” Jha told a group of reporters August 3. “They are not so sensitive when you have a low amount of virus and you’re not doing much spreading. But when you’re actually really infectious, you have large amounts of virus in your throat, elsewhere, and the test becomes much, much better.”
The huge problem right now
In the current test approach, by the time a person has symptoms, seeks a test, and then gets results back, they may have already infected many others. In fact, “the vast majority of PCR positive tests we currently collect in this country are actually finding people long after they have ceased to be infectious,” Mina tells Harvard Magazine. “The astounding realization is that all we’re doing with all of this testing is clogging up the testing infrastructure.”
And forget about contact tracing in places where infection rates are high, the experts say: By the time a person gets test results back, anyone they might have infected is already out there infecting others or has become sick and knows it.
In short, the PCR tests (which are different from antibody tests that reveal if someone was infected with Covid-19 in the past) are largely worthless given the scope of the pandemic and the delays in delivering results.
“Any Covid test that takes more than 72 hours to come back is useless and we shouldn’t pay a dime for it,” says Tom Frieden, MD, former director of the U.S. Centers for Disease Control and Prevention.
Here’s the big difference between PCR tests and the cheap at-home tests:
As a person contracts the coronavirus, it incubates for several days, building up the quantity of viral particles that leads to the Covid-19 disease and, as we know, outcomes ranging from no symptoms to death.
A less sensitive, rapid-return test will require more viral particles — a stronger developing infection — to positively detect it. A PCR test can detect an infection earlier up to 24 hours sooner than the at-home test, Mina explains. But the near-immediate answer from a less sensitive at-home test would still come sooner than the results of a PCR test by several days, given the PRC test’s processing lag, so a person with a positive test could self-isolate much more quickly.
“Any Covid test that takes more than 72 hours to come back is useless and we shouldn’t pay a dime for it.”
Growing need, especially for schools
Other scientists see the logic, and the need for an entirely different approach to testing, especially if children return to school and are tested regularly, as health experts suggest they should be. Also, as people migrate indoors in cooler weather, and the flu season ramps up, experts fear a double disease whammy that could be exacerbated by the inability to test broadly and quickly for Covid-19.
“As we inch closer to respiratory virus season (flu) I worry that if we don’t get the testing backlog/capacity issues worked out, it will be significantly amplified,” Saskia Popescu, PhD, an epidemiologist and adjunct professor of public health at the University of Arizona, says in a tweet.
Meanwhile, scientists are starting to question the FDA’s reluctance to green light the rapid at-home tests.
“Is the FDA’s reluctance to approve a rapid test another example of paternalism in medicine?” asks Natalie Dean, PhD, an epidemiologist and assistant professor of biostatistics at the University of Florida. “Are we so worried about a few false negatives that we sacrifice the chance to detect so many true positives? PCR tests are simply not fast enough right now.”
Among the keys to making rapid home tests successful is that they be ubiquitous, used on a regular basis by everyone, Jha says. If you can do that, there’s very good data and modeling, he says, “that really shows you can drive the disease way, way down.”