One in 10 people with Covid-19 may remain infectious after 10 days, research suggests.
The amount of time people who test positive for the virus have to isolate for has been cut to five days in England.
When announcing the cut, health secretary Sajid Javid cited UK Health Security Agency (UKHSA) data that showed around two-thirds of people were no longer infectious by the fifth day.
The UKHSA also found that around 5 per cent of people were still infectious after 10 days. But a new study, led by the University of Exeter, suggests the figure could be more than twice that.
Of 176 people who had tested positive with PCR tests, 13 per cent were found to potentially be infectious after 10 days.
Researchers used a newly adapted test that can detect whether the virus was potentially still active.
PCR tests can tell if someone has recently had the virus but cannot be relied on to tell if they are infectious.
The test used in the study gives a positive result only when the virus is active and potentially capable of transmission.
Some people were found to be potentially infectious for up to 68 days.
Professor Lorna Harries of the University of Exeter Medical School, who oversaw the study, said: “While this is a relatively small study, our results suggest that potentially active virus may sometimes persist beyond a 10 day period, and could pose a potential risk of onward transmission.
“Furthermore, there was nothing clinically remarkable about these people, which means we wouldn’t be able to predict who they are.”
The authors of the study said the new type of test should be used to protect vulnerable people.
Merlin Davies, the lead author, said: “In some settings, such as people returning to care homes after illness, people continuing to be infectious after 10 days could pose a serious public health risk.
”We may need to ensure people in those setting have a negative active virus test to ensure people are no longer infectious. We now want to conduct larger trials to investigate this further.”
The study was a collaboration between the University of Exeter Medical School, the Royal Devon & Exeter NHS Foundation Trust, and the NIHR Exeter Clinical Research Facility. It was funded by Animal Free Research UK and published in the Journal of Infectious Diseases.
Carla Owen, CEO of Animal Free Research UK, said: “The University of Exeter team’s discovery is exciting and potentially very important. Once more, it shows how focusing exclusively on human biology during medical research can produce results that are more reliable and more likely to benefit humans and animals.
She added: “The results also send a loud and clear message to the government to better fund modern medical research and make the UK a world leader in cutting edge, kinder science.”
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