Every American should get weekly coronavirus test

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 U.S. And it won’t be improved by the new $50 athome test made by startup Lucira Health Inc., which was given emergency authorization last 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, COVID19 lies low for several days before suddenly accelerating. It’s wellknown 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.

What we have instead is a terrible system that confuses and misleads. Last week, people were waiting for hours in long lines hoping to get a test they hoped would 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.

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 germspreading mingling seen at September’s infamous White House event. You’d still want to wear a mask when you visited your 88year-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.