People with Covid-19, the illness caused by the coronavirus, are most infectious about two days before symptoms begin and for five days afterward, according to a new analysis of previous research.

A few patients who are extremely ill or have impaired immune systems may expel — or “shed” — the virus for as long as 20 days, other studies have suggested. Even in mild cases, some patients may shed live virus for about a week, the new analysis found…

In September, France dropped its required period of isolation to seven days from 14 days, and Germany is considering shortening it to five days. (Isolation refers to people who are ill; quarantine refers to people who have been exposed to the virus and may become ill.)

Setting the isolation period at five days is likely to be much more palatable and may encourage more infected people to comply, said Dr. Muge Cevik, an infectious disease expert at the University of St Andrews in Scotland who led the new analysis, published in the journal The Lancet Microbe.