And because timing matters so much in Covid-19 detection, rapid tests can be more accurate than PCR for cutting down the risk of super-spreading events at private gatherings. They are also good for anyone planning to visit friends or relatives who are on chemotherapy or immune-suppressing drugs after an organ transplant, or who are over 80, or for whatever reason remain unvaccinated.
On the other hand, if you were infected at a party or restaurant last weekend, took a PCR test on Tuesday, and then go to have Christmas Eve dinner with your grandparents, you’re putting them at risk. A weekend exposure might not show up that early, and by Christmas you could be highly infectious. A rapid test right before your visit could pick up what that early PCR missed.
The PCR test was designed to amplify the viral genetic material—RNA—and can therefore pick up minute amounts. The rapid tests pick up viral proteins, called antigens, and since these are not amplified, it won’t pick up a new infection quite as early, and it won’t keep coming up positive after you’ve stopped being infectious.
Rapid tests are a good first course of action if you feel cold or flu symptoms. If a test is positive, you can start isolating yourself sooner and notify contacts, and soon it will be possible to take advantage of effective antiviral treatments such as Pfizer’s Paxlovid. If you have cold or flu symptoms but test negative, Adalja of Johns Hopkins recommends going to a pharmacy and getting a PCR test before you consider yourself cleared.
If you have no symptoms but a rapid test before an event turns up positive, you’ll have to skip that event no matter what. The experts agree, however, that if you’ve been vaccinated, you can isolate for 5 to 7 days, instead of waiting for 10 days, then take another test. That’s because vaccinated people are infectious for much shorter periods.
Most brands of home tests can detect omicron, though Adalja noted the Food and Drug Administration has reported that three brands—made by Meridian Bioscience, Applied DNA Sciences and Tide Laboratories—don’t work as well at picking up the new variant. Otherwise, he said, all brands are fairly interchangeable.
One problem is the rapid tests are regulated like a medical diagnostic test, and the experts say this has led to an onerous regulatory process that has limited supply and passed the cost to consumers. In much of Europe, rapid tests are regulated as a public health screening tool, which has allowed them to be free and easy to get for months.
The fact that home tests are hard to find and that New Yorkers are waiting in long lines is part of a policy failure. The Biden administration’s 500 million tests won’t be ready to ship by New Year’s, and a website has to be set up and work for people to submit their requests.
How can public health departments track the results of at-home tests? Tests often come with a QR code that makes it easy to report results, but even if people don’t follow through, having the information in the test-takers’ hands is probably more likely to save lives than it would be in the state health departments’ files. The test takers are in the best position to notify contacts, since most state-run contact tracing efforts have been scaled back or discontinued.
Rapid tests might become one part of pandemic response that people won’t mind keeping even after the disease becomes endemic and a big portion of the population stops social distancing and wearing masks. The immune-compromised may be at risk for some time, and testing can allow them to enjoy the kind of social life we all need.
This article was provided by Bloomberg News.