A new study identified a new, practical strategy for COVID surveillance on the part of larger groups of people through regular rapid antigen tests.

With frequent, regular rapid antigen testing, plus isolating people who test positive, organizations can cut the risk of out-of-control COVID outbreaks effectively and make long quarantines a thing of the past, according to the new study conducted by Yale epidemiologist.

This is possible even though rapid antigen tests are less accurate than gold-standard PCR tests. This is because rapid antigen tests deliver results fast, making up in speed for what they lack in accuracy. That gives them an edge when they’re used frequently to test groups of people.

“There’s been a lot of throwing up of our hands lately and saying, ‘What can we do?’ People think there’s no way to eliminate risk. But that’s not true,” says senior author Jeffrey Townsend, the Elihu Professor of Biostatistics at the Yale School of Public Health and professor of ecology and evolutionary biology at Yale University. “If you test frequently enough, you can repress transmission within a community.”

The study appears online in Communications Medicine.

In an October 2021 study that changed policy at the U.S. Centers for Disease Control and Prevention (CDC), Townsend’s team demonstrated that 14-day quarantines can safely be shortened to seven days if people test negative with a PCR test on the seventh day.

The current study suggests a way that groups can shorten quarantine even more.

Benefits of Rapid Antigen Testing

For the study, the researchers used public data and mathematical models to study three questions:

  • After a person leaves quarantine with a negative rapid antigen test, how likely are they to transmit COVID to others?
  • If they transmit COVID, how many people are likely to become infected?
  • How do 18 commercially available, FDA-authorized rapid antigen tests stack up against PCR tests in terms of accuracy?

Taking into account variations in different commercially available rapid antigen tests, the authors found that the ability of these tests to reduce post-quarantine transmission depends on how long quarantine lasts and how fast results come back. When the rapid tests are taken in relation to a person’s infection status—before, during, or after symptoms appear—is also important. Though less accurate than the PCR test, rapid antigen testing gives results in minutes, while a PCR test may take many hours or even days.

When testing to exit a two-day or shorter quarantine, the authors found, a negative quick-turnaround rapid antigen test can reduce COVID transmission more effectively than a 24-hour-turnaround PCR test.

“It turns out that the rapid antigen tests are basically as effective as PCR if there’s a day’s delay to get your PCR results,” Townsend says. “Notifying people that they’re sick is critical to them preventing further transmission.”

Determining Testing Intervals

With every-other-day testing, all rapid antigen test brands work to suppress COVID outbreaks, the authors found.

“Any transmission will probably peter out very quickly,” Townsend says.

Testing every three days was feasible with some rapid antigen tests, while others weren’t accurate enough to offer a clear picture.

Testing every four or five days, though, risked COVID spreading out of control.

With masking, ventilation, vaccines, and other related measures in place, the protection that frequent testing can offer is even stronger, Townsend said.

“If you’re doing this regular testing for sports teams and other people who are working closely together, you can give them a sense of assurance that it’s okay for them to be in that group,” he says. “It doesn’t mean no one’s going to get COVID-19. But it means that there’s not going to be these extended transmissions within groups. So, people can feel some sense of assuredness that their group, at least, is at relatively low risk.”

The study was funded by the Notsew Orm Sands Foundation, BHP, and BP.

The study’s first author was Chad R. Wells, a postdoctoral research associate with the Yale School of Public Health’s Center for Infectious Disease Modeling and Analysis (CIDMA).

Co-authors were Research Scientist Abhishek Pandey and Professor Alison P. Galvani, also of CIDMA; Seyed M Moghadas of York University in Toronto; Burton H. Singer of the University of Colorado Anschutz Medical Campus; Gary Krieger of NewFields E&E in Boulder and of the University of Colorado Anschutz Medical Campus; Richard J.L. Heron and David E. Turner, both of BP; Justin P. Abshire and Kimberly M. Phillips, both of BHP Petroleum; and A. Michael Donoghue of BHP Group. Dr. Townsend also holds appointments in the Program in Computational Biology and Bioinformatics and in the Program in Microbiology, both at Yale University.