Americans are still doing Covid-19 testing wrong. The kind of testing and contact tracing that scientists advocated in the spring to combat the virus isn’t working in the US. And it won’t be improved by the new $50 at-home test made by startup Lucira Health Inc., which was just given emergency authorization this week by the Food and Drug Administration.
That’s because a biological quirk of this disease means the current testing system misses the bulk of the cases in their most contagious period. But a different strategy would catch them. And we already have the technology to do it.
Once it’s in your body, Covid-19 lies low for several days before suddenly accelerating. It’s well-known that the virus has an incubation period of around five days, and possibly as long as 14, before symptoms appear. What’s not so well-known is that during most of its “quiet” phase, the virus is invisible to most tests. People are at the most risk of transmitting the disease a couple of days before symptoms start and a few days afterwards. That’s the stage a test needs to capture.
To combat the pandemic with testing, then, we need to test people once a week or more. That means we need a test that’s fast, easy, cheap and possible to distribute all over the country. The Lucira Health test is not that test, says Harvard epidemiologist Michael Mina. It’s too expensive, won’t scale up for massive, regular use, and requires a doctor’s prescription.
We could use the cheap antigen tests scientists have already developed. They’re as easy as a pregnancy test to administer and sensitive enough to show a positive result when a person is near peak infectiousness but has no symptoms. They could provide the kind of frequent testing that would end the pandemic.
A technology that looks even more promising is the use of wearable devices, which have been shown to pick up heartbeat changes that signal an infection before symptoms start. They can even signal an asymptomatic infection. I wrote about this in June, and this week more good results came out in the journal Nature Immunology. The inventor of the system, Stanford’s Michael Snyder, told me last spring that the devices can be made for just a few dollars and can continue to work for months — making them even cheaper than antigen tests.
What we have instead is a terrible system that confuses and misleads. This week, people are waiting for hours in long lines hoping to get a test they think will clear them to meet loved ones, some of them elderly and vulnerable, for Thanksgiving.
“Getting a PCR test today isn’t going to make you any safer for Thanksgiving,” Harvard’s Mina said at a media event eight days before the holiday.
Anyone early in the incubation phase is at risk of getting a false negative. Some people will have cleared an infection and no longer be able to transmit it; for them, the test will yield a false positive. Even people who are contagious now and test positive this week are unlikely to still be infectious next week, says Mina.
Mina says the New York Times wrongly asserts that existing scalable, cheap tests have only 30% sensitivity. The reporter used the wrong denominator, he says. The tests are missing people who are past their infectious period — not people who are still shedding virus and need to isolate.
Critics also say the tests haven’t been tested extensively in asymptomatic people, which is true. But there is convincing evidence out there that frequent use of cheap tests can catch enough infectious people to contain the virus.
That’s what officials are doing in Slovakia, where a program of mass weekly testing has already reversed an exponential spread of the virus. The program is more mandatory than might be acceptable in the US, but here, Mina says, we could create hundreds of millions of cheap tests and distribute them, 20 at a time, to US households. College campuses in many places have also seen success with regular twice-weekly screening tests of students.
One key point: Testing can reduce overall transmission, but it’s not precise enough to give individuals a free pass to socialize right away. People would still want to wear masks to the grocery store and avoid the sort of germ-spreading mingling seen at September’s infamous White House event. You’d still want to wear a mask when you visited your 88-year-old mom, or hold off seeing her for a little longer.
But catching and isolating a major fraction of infected people would curtail the pandemic so we could all go back to a more normal life within a few weeks.
Instead, the US is doubling down on strategies that aren’t working, says Mina. What we need is a strategy that is workable — “that won’t make people sit in line for two hours or stay home for 14 days because someone they walked by in the street was infected.”
It’s not just convenience at stake, says Muge Cevik, an infectious-disease doctor in the UK. She’s examined dozens of contact-tracing studies to show who’s the most at risk — poor people, people with public-facing jobs, people with multiple jobs, and people in crowded housing. The majority of them can’t afford to self-isolate at a contact tracer’s request.
Frequent testing would pick up new cases much faster than contact tracing could, and it would cut down on unnecessary quarantines of contacts who were not infected, but it would have to be combined with a system of financial relief so those who were infected could isolate without facing financial ruin.
“I get frustrated when I see people demanding the same things over and over … when we’re seeing that it’s not working,” says Harvard’s Mina. All you have to do is look at Massachusetts, where people are following the rules, the governor has enacted a strict indoor and outdoor mask mandate, and the state has assembled the country’s top contact-tracing program. “We still have exponential growth here and massive numbers of cases,” he says.
It’s time to admit the current approach isn’t working. The rollout of a $50 prescription home test isn’t going to fix it. In the months before vaccines become widely distributed, cheap wearables and tests given on a massive scale might just turn the tide, along with financial assistance to help infected people stay home. That’s actually following the science.
Bloomberg
