Yale study: CDC’s 5-day COVID quarantine is too short
In late 2021, the Centers for Disease Control and Prevention altered isolation protocols for people who tested positive for COVID-19. A study from researchers at Yale University suggests those protocols are not stringent enough to stop transmission.
“Given what we currently know about COVID-19 and the omicron variant, CDC is shortening the recommended time for isolation for the public,” the CDC said in December when it recommended quarantining for five days.
Rebecca Earnest, a doctoral student at the Yale School of Public Health, said five days may not be enough time to halt transmission of the disease.
The CDC’s guidelines do not include taking a rapid antigen test after the isolation period, but Yale asks its students to test after those five days. That created a data set for Earnest and her colleagues to study.
“Our question was relatively simple,” she said. “What percentage of people would we expect to remain positive via rapid antigen test on day five?”
A positive antigen test is a “proxy for infectiousness,” Earnest said. If your antigen test is positive, you are probably able to pass COVID on to someone else.
“There are probably some cases where people are no longer infectious, but in general, they've been shown to be a good proxy for infectiousness. And they are the best tool that we have, in terms of trying to safely have people leave isolation,” she said.
Earnest and her colleagues found that between 25 and 50 percent of the students tested remained positive on day five, with the number cut in half each additional day.
“So it's relatively high positivity on day five,” Earnest said.
Her conclusion is that “a five-day isolation period for the general population may be one to two days too short,” particularly with more transmissible variants like omicron and its subvariant, BA.2, and particularly in congregant settings like prisons and nursing homes.
When the CDC released its revised guidelines, agency Director Rochelle Walensky said, “these updates ensure people can safely continue their daily lives.”
“The omicron variant is spreading quickly and has the potential to impact all facets of our society,” she said in December. “CDC’s updated recommendations for isolation and quarantine balance what we know about the spread of the virus and the protection provided by vaccination and booster doses.”
But Earnest said the data based on those recommendations predated the omicron surge, which hit its peak in Connecticut on Jan. 10 when more than 31,000 new cases were reported in the state in a single day.
“This revised guidance came out at a time when omicron was beginning to surge in the U.S., and a lot of the data that those guidelines were based on was from a pre-omicron time period,” Earnest said. “We know that different COVID variants can have different infection dynamics, and those might affect how long people should remain in isolation.”
On Monday, the state reported 603 new COVID cases had been identified since Friday out of 24,226 tests for a positivity rate of 2.49 percent. At the same time, there was a net increase of five patients hospitalized with COVID for a total of 97 statewide.
While COVID infections have rapidly declined since the omicron surge, the revised CDC guidelines drew criticism from the public health community when they were released.
Gerald E. Harmon, president of the American Medical Association, said they are “not only confusing, but are risking further spread of the virus.”
“According to the CDC’s own rationale for shortened isolation periods for the general public, an estimated 31 percent of people remain infectious five days after a positive COVID-19 test,” he said in January. “Physicians are concerned that these recommendations put our patients at risk and could further overwhelm our health care system.”
But Earnest said the guidelines are not completely unreasonable.
“The decision-making behind this made some sense because what they're really trying to do is weigh the burden of keeping people in isolation for an unnecessarily long period of time — it has big social and economic consequences — with the risk of releasing people too early, and then they go on to spread COVID through their community,” she said.
The CDC’s guidelines do call for masking for an additional five days “when around others to minimize the risk of infecting people they encounter,” which Earnest said would help mitigate the spread of the virus from patients who are still infectious after five days.
She questioned, however, how many people would follow that masking guideline.
“We all know that human behavior varies a lot,” Earnest said. “I think it's unclear how much people actually adhere to that. But if someone did come out of isolation on day five, they're still positive, but they're really good about masking, social distancing, that would minimize the risks he would pose to others.”