Vaccinated people can spread the Delta variant. But experts disagree whether those without symptoms should be tested

Ashley Nicolas prepared a COVID-19 test for Janaiyah Brown, 8, at a drive-through testing site at Revere High School.Erin Clark/Globe Staff

Edy Rees had a sore throat. Two years ago, even a month ago, such a minor symptom would not have seemed portentous. But late last month the 78-year-old Roslindale resident was worried about COVID-19.

Scientists have recently discovered that even vaccinated people with mild symptoms may spread the coronavirus. Rees, who is fully vaccinated, spends a lot of time with a sick sister, and she wanted to know if she was at risk of infecting her vulnerable sibling.

So Rees joined the thousands of people in Massachusetts — 50 percent more than a month ago — who are seeking COVID-19 tests. And she found it more complicated than expected.

The demand for COVID-19 tests has been growing, at a time when the state’s success at fully vaccinating 64 percent of the population might make testing seem less urgent.

But as with so much in the pandemic, the ground is shifting again. The highly transmissible Delta variant of the virus, now dominant here and elsewhere, has been pushing up case counts nationwide, primarily but not exclusively among those who are not vaccinated.

In Massachusetts, the number of new cases has been increasing since mid-July. The uptick raises questions about whether testing, still well below the January peak, should be ramped up again to better track the infection and limit its spread.

“Without testing we cannot see the virus,” said Dr. Michael Mina, an epidemiologist at the Harvard T.H. Chan School of Public Health. “Bringing back testing is going to become central to our efforts in this phase.”

But the state Department of Public Health recommends tests only for those who have symptoms or recent contact with an infected person, although it does provide tests to asymptomatic people at 29 locations.

Dr. Ezekiel J. Emanuel, vice provost for global initiatives at the University of Pennsylvania, called for more screening of asymptomatic people “just to understand that situation much better.” Speaking Tuesday at a media briefing by the Infectious Diseases Society of America, Emanuel said asymptomatic people should be tested to monitor the evolution of new variants.

The number of molecular tests — the most common type — performed in Massachusetts has climbed to a seven-day average of roughly 30,000 per day, up from 20,000 per day in early July. That still doesn’t come close to the state’s testing peak in late January, when nearly 100,000 tests were conducted each day.

In Boston, COVID-19 testing has risen 34 percent in the past two weeks, reaching the highest level in the past four to six weeks, said Marty Martinez, the city’s chief of health and human services.

“We’ve done a lot of work with our health centers and our community organizations to make sure testing is accessible across our city,” he said.

Likewise, Cambridge has expanded its free testing program for residents, city officials said, now offering testing three times a week at two locations. And the state has extended its 29 free “Stop the Spread” testing sites through Sept. 30. They were originally scheduled to shut down on June 30.

Some of the test-seekers, such as Rees, are concerned about symptoms; others may have been exposed to infected people or need proof that they’re not infected for business or travel.

The state’s “Find a COVID-19 Test” website lists 466 locations, including the “Stop the Spread” sites offering free tests to anyone. Spokespeople for CVS and CareWell Urgent Care, which run numerous testing sites, say they are able to keep up with the growing demand.

A spot check of testing sites in the Boston area found a substantial number of available appointments, although the pharmacies were often fully booked for days. A number of sites also offer walk-up or drive-through testing without an appointment, but customers are advised to call ahead to be sure.

When Rees, the Roslindale woman, checked the CVS stores near her home, they were all booked. Her sore throat, likely the result of smoke pollution from the West Coast wildfires, had already abated on Thursday when she finally called the Mattapan Community Health Center, which quickly scheduled an appointment.

“That was such a relief. They were so easy to deal with,” Rees said of the health center. “The list that mass.gov publishes should have the easiest ones first. Somebody just trying to find a test doesn’t have time to call CVS for hours to find out that’s not going to be possible.”

CVS, Walgreens, and CareWell Urgent Care require test-seekers to have a specific reason — such as symptoms, contact with an infected person, or international travel — before they will schedule a test. Those who don’t meet eligibility criteria have to pay out of pocket, ranging from $105 to $210, depending on the site and the test.

However, the state’s 29 Stop the Spread sites offer free tests whether or not a person has symptoms and requires no insurance information. (There is no separate online list of those 29 sites, but they tend to be run by hospitals, health centers, or a company named Transformative Health. To find free tests, check the “Show Advanced Filters” box on the search page of the Massachusetts “Find a COVID-19 Test” site.

Additionally, home tests are available at retail stores. BinaxNOW and Ellume ($24 and $30, respectively, at CVS) provide results in 15 minutes. Other home tests are merely kits for collecting a sample at home and mailing it to a laboratory, with results in a couple of days. The state Department of Public Health provides one such test, Pixel, for free to adult residents who live or work in a congregate setting, have symptoms, or meet other criteria.

Dr. Cassandra Pierre, medical director of public health programs at Boston Medical Center, cautioned that the rapid at-home tests can miss smaller viral loads that a molecular test would detect and work best when performed repeatedly. People who spend time around the unvaccinated or immunocompromised might consider testing themselves regularly, she said.

“Doing this test more often gives you the opportunity to pick up a virus that may have been undetectable the first time you tested,” Pierre said.

Pierre urged people, including vaccinated people, to get tested if they don’t feel well. “Please don’t ignore your symptoms and attribute them to a summer cold or allergies,” she said.

But she didn’t see any purpose in testing people without symptoms or exposure.

Dr. Amesh A. Adalja, a senior scholar at the Johns Hopkins Center for Health Security, agrees with Pierre, seeing little value in testing asymptomatic people.

“The fact that breakthrough infections are mostly mild really makes it hard to see what value is gained by finding them,” he said in an e-mail.

But William Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, called testing one of the “arrows in your quiver” in the fight against COVID-19. Vaccination is by far the most powerful weapon, he said, but other methods must be deployed as well.

Hanage’s colleague, Mina, has long argued that tests should be regarded as a public health tool rather than a medical procedure to benefit an individual.

“Nobody gets a test in the hope that it will make them feel better,” he said. “It’s to ensure we’re not a danger to our neighbor.”

Universities have already demonstrated the effectiveness of testing programs, Mina noted. Those that conducted regular testing prevented major outbreaks, long before vaccines were available.

The state Department of Public Health declined to make an expert available to discuss its response to the Delta variant, but in an e-mail confirmed that its recommendation stands: Only people with symptoms or exposure to a COVID-19 case need testing.

Yet the state recently announced a requirement, starting Aug. 12, for weekly testing of staff in congregate care settings.

And Kerin O’Toole, spokeswoman for the Massachusetts League of Community Health Centers, said in an e-mail that “the important focus now is on asymptomatic testing” in discussions among health officials and providers.

“The news that asymptomatic, vaccinated individuals can spread the virus is so new — all of us (health care providers, public health officials, etc.) are just starting to get our heads around that fact,” she wrote.