The reason the coronavirus variant first identified in the UK is more transmissible than earlier versions of the virus may be that it spends more time inside infected people, giving them more time to spread the virus, according to a small study.
Researchers measured viral loads daily in 65 patients with Covid-19, including seven who were infected with the UK variant.
The amount of virus carried by patients was similar in the two groups.
But among individuals infected with the variant designated B.1.1.7, the average duration of infection was 13.3 days, compared to 8.2 days in those infected by an older version of the coronavirus.
The time until patients' viral loads peaked was also longer with the UK variant: 5.3 days, versus 2 days with earlier variants.
"The findings are preliminary, as they are based on seven B.1.1.7 cases," the researchers cautioned in a report posted without peer review on a Harvard University website.
"However, if borne out by additional data, a longer isolation period than the currently recommended 10 days after symptom onset may be needed to effectively interrupt secondary infections by this variant," they said.