Rapid antigen testing is just as effective in preventing COVID-19 outbreaks as polymerase chain reaction, or PCR, tests when used as part of a regular screening program, according to the National Institutes of Health.

When used individually, PCR tests are more sensitive than antigen tests, particularly early in infection. But a “highly anticipated” study funded by the agency now shows that both testing approaches can give 98% sensitivity when used every three days for screening. 

“Because antigen tests at the point of care or at home can deliver immediate results and are less costly than laboratory tests, these results suggest that they could be a highly effective screening tool to prevent disease outbreaks,” the NIH announced Thursday.

In its attempt to halt a shocking rate of illness and death due to COVID-19 in long-term care settings, the U.S. government began shipping free, point-of-care rapid antigen testing systems to nursing homes and assisted living communities in the fall of 2020. But some users voiced concerns about the rate of false positive results when compared with PCR testing.

The new findings strengthen the case for regular rapid antigen testing programs at the point of care, NIH said.  

“These results show, for the first time, that testing at least twice per week with rapid antigen tests has comparable performance with PCR testing and maximizes the likelihood of detecting people infected with SARS-CoV-2.”

The comparison

The researchers compared three COVID-19 viral testing modalities — PCR testing of saliva, PCR testing of nasal samples and rapid antigen testing of nasal samples — in 43 adults newly infected with SARS-CoV-2. They captured daily test results across the entire course of infection. The study lasted from early December 2020 through spring 2021. 

Test sensitivity was estimated based on test frequency. Investigators found that testing every three days achieved better than 98% sensitivity to detect infection, whether rapid antigen tests or PCR tests were used, reported Christopher B. Brooke, Ph.D., from the University of Illinois at Urbana-Champaign, and colleagues. When testing frequency was reduced to once per week, however, nasal and saliva PCR testing sensitivity remained high, but antigen test sensitivity declined to 80%.

Full findings were published Wednesday in the Journal of Infectious Diseases.