Coronavirus testing in the U.S. is declining. Experts aren’t sure why.


By Richard Fausset


The number of coronavirus tests administered daily in the United States has been trending downward for more than two weeks. And though experts say the trend is too fresh to set off major alarm bells, the decline raises the possibility that testing has reached a ceiling at a time when scientists say the nation should be conducting millions more tests per day to help stop the spread of the virus.


On Jan. 18, the seven-day average of daily new tests reached an all-time high of more than 2.1 million, according to the COVID Tracking Project. On Thursday, it was about 1.7 million.

Maintaining a level of at least 2 million tests per day is considered an important threshold by public health experts, who say that it is a level of testing that will allow them to identify most people with symptoms, as well as two people with whom each sick person has been in close contact.


This dip coincides with a downturn in another important coronavirus metric: the seven-day average of new reported coronavirus cases, which was down 57% Thursday compared with its peak on Jan. 8.


When the number of tests performed and cases reported go down at the same time, public health experts want to know if the dip in new cases is tied to the fact that fewer tests are being performed — the theory being that “If you don’t test, you don’t find cases,” as Dr. Jodie Guest, a public health researcher at Emory University, put it recently.


For now it seems the number of new cases is indeed falling, said Dr. Ashish Jha, dean of the Brown University School of Public Health, who noted that the percentage of positive tests is also on the decline. “That’s why I’m convinced the decline is real,” Jha said in an interview Friday night.


The decline, unfortunately, is also relative. Friday’s seven-day average of about 130,953 daily reported cases in the U.S. is still significantly higher than peaks in the spring and summer.

The COVID crisis is still with us. So why are the testing numbers going down?


Dr. Emily Martin, an associate professor of epidemiology at the University of Michigan, said that the recent dip in testing should come with “lots of caveats on what exactly it is we can take away” from the trend. It may be, she said, that testing spiked in January, possibly caused by people returning to jobs and schools after holiday breaks and being subjected to mandatory testing.


But Martin and other experts say that the numbers could also reflect a complacency about testing, as vaccine distribution is ramping up.


It is also possible that the dip reflects the burden on public health offices that are being asked to both administer vaccines and tests at the same time — and that vaccinations, in some cases, are taking precedence. The seven-day average of vaccinations has been on the rise, topping 1.3 million in recent days and approaching the Biden administration’s goal of 1.5 million doses per day.


“I do know that there are testing facilities that have been shifting their focus to vaccinations right now,” Guest said. “And I do wonder if the numbers we’re seeing go down are based on some shifting of priorities.”


And that is not particularly good news: Experts say that widespread testing must continue to be part of the fight against the pandemic, because scientists don’t know exactly how effective most of the vaccines are at slowing the spread of the virus. Vaccine trials, in the interest of speed, were intended primarily to study how effective the inoculations are against stopping the onset of severe COVID-19 disease and not whether they would prevent the transmission of the virus.


There was some progress on that front this past week, with a study that showed that the vaccine developed by the University of Oxford and AstraZeneca has the potential to slow the transmission, according to researchers at the university.

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