Published: 19 August 2022
A new NIHR funded study of 57 people with mild COVID-19 estimates how long people are infectious for and when they can safely leave isolation.
The research, which is led by Imperial College London and published in The Lancet Respiratory Medicine journal, is the first to unveil how long infectiousness lasts for after natural COVID-19 infection in the community.
The study team conducted detailed daily tests from when people were exposed to SARS-CoV-2 to look at how much infectious virus they were shedding throughout their infection.
The findings suggest that in people who develop symptoms, the majority are not infectious before their symptoms develop. Two-thirds of these cases are still infectious, five days after their symptoms begin. They also suggest that while lateral flow tests do not detect the start of infectiousness well, they more accurately identify when someone is no longer infectious and can safely leave isolation.
Study author, Professor Ajit Lalvani, Director of the NIHR Health Protection Research Unit in Respiratory Infections at Imperial, said: "Before this study we were missing half of the picture about infectiousness, because it’s hard to know when people are first exposed to SARS-CoV-2 and when they first become infectious. By using special daily tests to measure infectious virus (not just PCR) and daily symptom records we were able to define the window in which people are infectious.”
The researchers recommend that people with COVID-19 isolate for five days after symptoms begin and do lateral flow tests from the sixth day. If tests are negative two days in a row, it is safe to leave isolation. If a person continues to test positive, they should remain in isolation while testing positive but may de-isolate on the 10th day after their symptoms began.
Current NHS guidance suggests that people should try to stay at home and avoid contact with others for just five days.