Majority of symptomatic Covid-19 patients still infectious after five days

  • Date: 22 August 2022

TWO-THIRDS of symptomatic Covid-19 patients are still infectious five days after their symptoms begin, according to the first “real-world” study into the disease onset.

Researchers with Imperial College London conducted detailed daily tests on 57 people with mild Covid, from first exposure to SARS-CoV-2 to determine how much infectious virus they were shedding throughout their infection.

The findings published in The Lancet Respiratory Medicine suggest that the majority of subjects were not infectious before their symptoms developed, but two-thirds remained infectious five days after symptoms began. The research also determined that lateral flow tests are not effective in detecting the start of infectiousness but do more accurately identify when someone is no longer infectious and can safely leave isolation.

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. Anyone who continues to test positive should remain in isolation while testing positive but may de-isolate on the 10th day after their symptoms began.

Professor Ajit Lalvani, director of the NIHR Health Protection Research Unit in Respiratory Infections at Imperial and a study author, 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.”

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