The US Centers for Disease Control and Prevention released some of the data backing up its decision to shorten recommended isolation and quarantine periods for people who test positive for the coronavirus or who are exposed to someone who has it.
In updates to its recommendations released Tuesday, the CDC said that if people have access to a Covid-19 test and want to take one, the best approach is to use a rapid test toward the end of their five-day isolation period.
It cites a few sources in explaining the recommendations.
“Data, including a review of 113 studies from 17 countries, show that most SARS-CoV-2 transmission occurs early in the course of infection,” the CDC says. “Infectiousness peaks around one day before symptom onset and declines within a week of symptom onset, with an average period of infectiousness and risk of transmission between 2-3 days before and 8 days after symptom onset,” the agency adds, linking to two sources.
One analysis the CDC cites, published in the Annals of Internal Medicine, dates to September 2020 and looks at what was detailed in other studies.
The second source, a review of 113 studies, published in the Lancet medical journal on Dec. 20, 2021, says that review that showed genetic material from the virus can be detected up to six days before people develop symptoms and as long as two weeks afterwards.
“Studies using viral cultures show that, although patients can remain RNA-positive for weeks after symptom onset, live virus cannot be cultured from specimens collected later than 9 days after symptom onset, suggesting that the mean period of infectiousness and risk of transmission could be restricted to the period between 2 and 3 days before and 8 days after symptom onset,” says the Lancet study, conducted by Rosanna Peeling of the London School of Hygiene and Tropical Medicine and colleagues.
The CDC notes that the data comes from studies done before the Omicron variant was circulating. “The science is evolving, particularly for the Omicron variant, and some reports suggest that compared with previous variants, Omicron has a shorter incubation period (2-4 days), defined as the time between becoming infected and symptom onset.” It links to those studies, as well.
“Hospitalization and death rates are much lower for vaccinated people for all SARS-CoV-2 variants; preliminary data from South Africa suggest that hospitalization and death rates are lower for people infected with Omicron compared with other variants,” the CDC adds, citing a study from a private South African hospital group published in the Journal of the American Medical Association.
“Early estimates of lower vaccine effectiveness against symptomatic infection due to Omicron after the Pfizer-BioNTech primary series suggest that booster doses are important to improve protection from hospitalization and death due to infection with the Omicron variant,” the CDC adds, referring to a Dec. 14 pre-print of work led by the UK Health Security agency.