What we knowStudies conducted before the emergence of Omicron demonstrated that people with Covid-19 were most likely to spread the virus in the few days before and after developing symptoms. The Centers for Disease Control and Prevention cited these findings when explaining its decision to shorten its isolation guidelines late last year. Research also suggests that rapid antigen tests are most likely to be positive early in the course of illness, but there is considerable variation. That percentage declined over the following days, but an estimated 20 percent were still positive on Day 11, according to the study, which has not yet been published in a scientific journal. “That’s a pretty good indication that they’re likely to be infectious,” said Dr. Amy Barczak, an infectious disease expert at Massachusetts General Hospital, who found that 25 percent of people still had viable virus on Day Eight or beyond.

Source: New York Times May 31, 2022 18:21 UTC