Coronavirus testing is down by at least a third from its peak during the winter holidays in the greater Washington region, sparking concern among public health experts who worry that lower testing numbers mean officials could be late to recognize a future surge in cases or the next vaccine-resistant variant.

There are several reasons for the drop. As state and local governments focus on coronavirus vaccine distribution, they have shifted resources away from large-scale testing events. Medical professionals say fewer people report experiencing symptoms that cause them to seek tests. And pandemic fatigue has set in, diminishing public enthusiasm for getting tested.

But a year into the pandemic, public health experts urge individuals to remain vigilant about getting tested — not only to protect themselves and the health of those around them, but also to help officials understand the extent of community spread of the virus and how it is changing over time.

“It’s as if we’re in a major paradigm shift in this pandemic and the world has gone from the world of testing to the world of vaccination,” said Boris Lushniak, a former acting U.S. surgeon general who is dean of the University of Maryland School of Public Health. “But the problem is — and this is a major problem — we can’t give up on testing. . . . If we give up on testing, this wildfire of covid-19 will be spreading to our communities as we’re trying put it out in different forests.”

Governors and public health officials closely monitor the number of new infections compared with the number of tests being conducted to help them decide whether it’s safe to relax restrictions on activities such as indoor dining and gatherings.

They generally aim for a sustained “positivity rate” of 5 percent or less, the benchmark set last spring by the World Health Organization to guide governments in reopening.

Last week, D.C. and Maryland reported positivity rates below that benchmark — a seven-day rolling average of 4.6 percent in the District and 3.7 percent in Maryland. In Virginia, the positivity rate was 7.8 percent.

Officials say they would need to ramp up testing if the number of tests declined as the number of positive infections grew, which would indicate not enough people with symptoms and without are being tested to accurately reflect the infection rate — but at the moment both numbers are falling. All three jurisdictions have reported a drop in infections in recent weeks.

Still, officials noted that testing numbers are on par with the levels seen last fall and far greater than last summer, when testing sites saw long lines and high demand.

The metrics helped Virginia Gov. Ralph Northam (D) decide to eliminate a midnight to 5 a.m. curfew as of this Monday, a measure he put in place in mid-December when cases were on the rise. Although Virginia only briefly achieved a 5 percent positivity rate last fall, he said the numbers are again moving in the right direction.

“We still have the capacity to do really as many tests as we need to do, but less people are symptomatic, and when less people are symptomatic there are less requests for their providers to do the test,” he said in a recent news conference.

In fact, testing in Virginia and Maryland is down by about a third after a spike in infections that began around the winter holidays and continued until recently.

A similar scenario has played out in the District, where the number of tests conducted per capita each week fell by more than half from its late November peak.

The District’s case rate on Feb. 21 finally fell below 15 average daily new cases per 100,000 people, a metric that the city has been targeting for months.

But Health Director LaQuandra Nesbitt raised the possibility that the rate looked artificially low because fewer people are getting tested and fewer asymptomatic cases are being identified.

Public health officials in the District and Prince George’s County noted that inclement weather in February and testing center closures over the Presidents’ Day holiday probably prevented some people from getting tested as well.

Lynn Goldman, dean of George Washington University’s Milken Institute School of Public Health, said widespread community testing is critical to detecting variants, which spread more easily and may not be stopped by available vaccines.

“Our danger has to do with relaxing our vigilance when we’re becoming more and more aware of variants that may be able to escape naturally acquired and vaccine-generated immunity,” she said. “We need to be very vigilant. Those mutations can arise anywhere.”

In the early months of the pandemic, tests were scarce and difficult to get, but slowly, mass testing events became the norm and patients began to acquire tests from their doctors and pharmacies.

Then the vaccine became available, beginning in mid-December for health-care workers, and later expanding to others. Lushniak said health departments with limited resources and personnel were torn.

“What do you do? Do you test or do you vaccinate?” he said. “The answer is you’ve got to do both.”

The Virginia Health Department made a concerted effort to shift resources from tests and focus on vaccinations as soon as doses became available in late December, said Parham Jaberi, chief deputy commissioner at the department.

“We just haven’t had the personnel or capability to have that testing strategy sustained as the focus has shifted to the vaccine,” he said, noting that testing in targeted areas is still happening.

In Maryland, a large-scale testing site at Six Flags in Prince George’s County was built for 2,000 tests daily but was down to 300 to 400 tests, prompting the state to convert it to a mass vaccination site on Feb. 5, said Mike Ricci, spokesman for Gov. Larry Hogan (R). Mass testing sites at the Baltimore Convention Center and in a parking lot near the State House in Annapolis are still open. National Guard members were deployed to testing sites, replacing nurses needed to serve as vaccinators, Ricci said.

In Montgomery County, where testing has fallen by half since December, Health Officer Travis Gayles said vaccinations have “taken up all the oxygen in the room,” distracting residents from getting precautionary tests or being interested in whether they have the virus.

As a result, state and county officials are developing communication campaigns to “remind people of the value of testing,” he said.

In Prince George’s County, which has been hit hard by the virus, testing sites in Clinton and Largo have been closed since December, and staff redirected to focus on vaccinations. Testing sites in Hyattsville and Fort Washington remain open.

The county site closures were driven in part by a more than 30 percent drop in demand, from a record high of 40,904 in the week of Jan. 3 to 26,995 the week of Feb. 14.

At the same time, new cases declined by about 45 percent, said Ernest Carter, the county health officer, adding that there are “still sufficient numbers of tests being conducted in Prince George’s County each week to adequately detect for virus spread.”

But Neil J. Sehgal, an assistant professor of health policy and management at the University of Maryland School of Public Health, said it’s difficult to know how many tests are enough.

Most of the graduate students he works with regularly got tested in 2020, but none of them have so far this year, Sehgal said, a change he attributed to pandemic fatigue and fewer testing sites available.

“Like any public health prac­tices, if it is hard to do then it is easier to ignore,” he said. “It is not enough to say, ‘This is something good for you so you should do it.’ ”

Erin Cox, Rebecca Tan and Julie Zauzmer contributed to this report.