In a new study, Yale epidemiologists have come up with a more realistic strategy for COVID surveillance for companies, groups, schools, and communities.
With frequent, frequent rapid antigen (RA) testing, plus isolating those who test positive, organizations can cut the risk of COVID-19 outbreaks, say the researchers. effectively spiraling out of control and making long quarantines a thing of the past, the researchers said.
This is doable although the RA test is less accurate than the gold standard PCR test. Reason? RA tests provide quick results, making up for what they lack in accuracy. That gives them an advantage when they are used frequently to test groups of people.
“Recently, a lot of people raise their hands and say, ‘What can we do?’ People think there’s no way to eliminate risk. But that’s not true,” said senior author Jeffrey Townsend, Elihu Professor of Biostatistics at the Yale School of Public Health and professor of ecology and evolutionary biology at Yale University. “If you test often enough, you can stop transmission in the community.”
The study appeared online in Communication Medicine.
In an October 2021 study that changed policy at the US Centers for Disease Control and Prevention (CDC), Townsend’s team demonstrated that a 14-day quarantine period can safely be withdrawn. shortened to seven days if people test negative by PCR on Saturday.
The current study suggests a way that groups could shorten quarantine even further.
Rapid antigen testing may provide a way forward
For the study, the researchers used public data and mathematical models to investigate three questions:
- After a person leaves quarantine with a negative RA test, how likely are they to pass COVID to others?
- If they transmit COVID, how many people are likely to become infected?
- How do 18 commercial, FDA-authorized RA tests stack up in terms of accuracy of PCR tests?
Taking into account variations in different commercial RA tests, the authors found that their ability to reduce post-isolation transmission depends on (1) the length of isolation and (2 ) how quickly the results come back. When RA tests are done about a person’s infection status – before, during, or after symptoms appear – are also important.
Speed is key.
Although less accurate than PCR tests, RA tests give results in minutes, while PCR tests can take hours or even days, hindering real-time detection of who is infectious. After all, people can contract or transmit COVID while they wait for results.
When tested for exiting a two-day or shorter quarantine, the authors found that a negative rapid turnaround RA test could more effectively reduce COVID transmission than a 24-hour cycle PCR test.
“It turns out that rapid antigen tests are just as effective as PCR if you have a one-day delay in getting PCR results,” Townsend said. “Informing people that they are sick is very important for them to prevent further transmission.”
How often should testing happen?
The authors found that, with daily testing, all brands of RA testing – even the less accurate ones – worked to contain the COVID outbreak.
“Any possible transmission would quickly disappear,” Townsend said.
Testing every three days is possible with some RA tests, while others are not precise enough to provide a clear picture. However, getting tested every four or five days carries the risk of COVID spreading out of control.
With shielding, ventilation, vaccines and other related measures, says Townsend, the protection that regular testing can offer is even stronger.
“If you are doing this routine test for sports teams and other people who work closely together, you can give them a sense of assurance that they are on that team,” he said. “That doesn’t mean nobody gets COVID-19. But it does mean that there won’t be these extended transmissions in groups. So everyone can rest assured that their team is, at the very least, relatively low risk.”
The study was funded by the Notsew Orm Sands Foundation, BHP and BP.