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Frequent Covid Tests Urged to Help Curb Spread of Delta Variant

Aug. 2, 2021, 9:30 AM

The highly contagious delta variant has prompted some infectious disease physicians to call for ramped-up Covid-19 testing to prevent infected, vaccinated people from spreading the virus unknowingly.

“We need a lot more testing. And we need to think about how do we scale up testing in an effective way,” Carlos del Rio, executive associate dean and epidemiologist at Emory University, said. “Identifying people before they infect others, I think it’s critically important.”

The Centers for Disease Control and Prevention on Friday released findings that people infected with the delta variant in Cape Cod, Mass., carried similarly high loads of SARS-CoV-2, regardless of whether they were vaccinated. The agency revised its guidelines to recommend that fully vaccinated people wear masks indoors in areas of high or substantial transmission, and that they get tested three to five days after potential or suspected exposure to Covid-19.

Some physicians say more frequent testing would be helpful even if they haven’t had contact with an infectious person.

Denmark, the U.K., Germany, and many other countries have distributed rapid home tests widely so their residents can know in 20 minutes or less whether they’re infectious and should stay home, Eric Topol, director and founder of the Scripps Research Translational Institute in La Jolla, Calif., said.

“This has been the biggest missing component of our total strategy in the United States,” he said.

Abbott Laboratories makes an at-home test called BinaxNOW that’s easy to use and available at CVS, Walgreens, Amazon, and other major retailers. But at $24 for a two-pack, Topol said it’s too costly for people to use everyday to determine if they should go to school, work, or elsewhere. “That’s a good test. It’s just that it’s ridiculously expensive,” he said.

“In an ideal world, everyone would be testing multiple times a week until vaccination rates improve, but that is clearly not feasible and would be rejected by many on cultural/ideological grounds,” said Christopher Brooke, an assistant professor of microbiology at the University of Illinois, who supports the CDC’s new testing guidelines.

The first steps toward at-home Covid-19 testing in the U.S. go back to May 2020, when the Food and Drug Administration authorized tests with the option of using home-collected saliva samples. The government should have picked some of the best tests and made hundreds of millions available, Topol said.

“In January we didn’t know there was going to be a delta. We should have assumed the worst. And now we were seeing that and we’re not ready. We’re caught flat footed,” he said.

New Guidelines

Testing in the U.S. dropped dramatically in the spring as more people became vaccinated, according to a Johns Hopkins University tracker. But almost every state has seen an increase as the delta variant has led to surges, particularly in areas where the vaccination rate is low.

Previously, the CDC didn’t recommend testing “if a fully vaccinated individual (assuming they are not a healthcare worker) remained asymptomatic after an exposure,” Kimberly E. Hanson, an infectious diseases specialist at the University of Utah who co-authored the Infectious Diseases Society of America’s testing guidelines, said in an email.

Under the new recommendations, fully vaccinated people can still refrain from routine screening testing when feasible, she said.

For the time being, vaccinated individuals probably only need to test if they have a known exposure, are symptomatic, or are going into a high-risk setting, Brooke said. “This is more important where virus is more prevalent but I can’t provide a magic number in terms of case frequencies.”

Del Rio said the frequency at which someone should get tested will depend on what someone is doing and their risk level.

“If I’m going to go on vacation with my young kids who may have been out partying, I may decide before I go and spend time with them that maybe we’ll get tested before we go,” he said.

Not Unusual

The Covid-19 vaccines were designed to protect against illness and death—not infection—so the possibility of vaccinated people getting the disease was well-known long before the delta variant arrived. Vaccinated people are less likely to get sick compared to those who are unvaccinated. Nearly all of the new hospitalizations and deaths are among unvaccinated people.

“This was an unexpected benefit and a bit of a surprise that they would work that well in the nose where the gradient between the serum and tissue is much higher,” Barney S. Graham, deputy director of the National Institute of Allergy and Infectious Diseases Vaccine Research Center, said at a recent National Academy of Sciences event.

“So this is not an unusual thing for people to be infected after a vaccine designed to protect the lung,” he said.

Before delta emerged, evidence clearly indicated that vaccinated people are much less likely to transmit Covid-19 if infected, Brooke said. But the latest CDC data suggests vaccination may be less effective at reducing viral shedding when delta is involved—meaning there’s a greater risk vaccinated people may transmit the virus to others.

“What you’re seeing now is as virus variants drift a little further away from the original strain, we are having some people who were vaccinated develop symptomatic infection. And what that means in almost every case is that they’re developing the sniffles,” Graham said.

Based on that, Brooke said it’s “totally reasonable to recommend that vaccinated individuals get tested if they have been exposed and step up the use of [non-pharmaceutical interventions] such as mask wearing.”

Testing recommendations are likely to change, however, depending on future variants and the prevalence of community spread.

“Vaccination remains highly effective at preventing severe disease, hospitalization and death from SARS-CoV-2 including with the delta variant,” Hanson said. “However, the Cape Cod outbreak did show that it is possible for vaccinated individuals to develop symptomatic infection after vaccination with the delta variant.”

To contact the reporter on this story: Jeannie Baumann in Washington at

To contact the editors responsible for this story: Fawn Johnson at; Alexis Kramer at