UK: Study by Imperial College reveals new info on how long people with Covid-19 are infectious

For the first time, a study led by Imperial College London and published in The Lancet Respiratory Medicine journal reveals how long infectiousness persists after a community member contracts COVID-19 naturally.

ANIUpdated: Friday, August 19, 2022, 04:47 PM IST
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London: How long someone is contagious and when they can safely be discharged from isolation were the subjects of a recent study on 57 people with mild COVID-19.

For the first time, a study led by Imperial College London and published in The Lancet Respiratory Medicine journal reveals how long infectiousness persists after a community member contracts COVID-19 naturally. From the time participants were exposed to SARS-CoV-2, the research team carried out meticulous daily testing to determine how much contagious virus they were shedding over the course of their infection.

The results indicate that most symptomatic individuals are not infectious before symptom onset, but that two-thirds of cases are still infectious five days later.

Additionally, they contend that while lateral flow tests are less effective in detecting the onset of infectiousness, they do a better job of determining when a person is no longer contagious and may safely be released from isolation.

Study author, Professor Ajit Lalvani, Director of the NIHR Health Protection Research Unit in Respiratory Infections at Imperial, said: "We closely monitored people in their homes from when they were first exposed to the virus, capturing the moment when they developed infection through until they ceased being infectious. 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 viruses (not just PCR) and daily symptom records we were able to define the window in which people are infectious. This is fundamental to controlling any pandemic and has not been previously defined for any respiratory infection in the community."

"Combining our results with what we know about the dynamics of Omicron infections, we believe that the duration of infectiousness we've observed is broadly generalisable to current SARS-CoV-2 variants, though their infectious window may be a bit shorter. Our evidence can be used to inform infection control policies and self-isolation guidance to help reduce the transmission of SARS-CoV-2."

Co-author, Dr. Seran Hakki also from Imperial's National Heart and Lung Institute, said: "There is no longer a legal requirement to self-isolate if you test positive for COVID-19, but most people still want to isolate until they are not infectious. Despite this, there is a lack of clarity on how to come out of self-isolation safely. Our study is the first to assess how long infectiousness lasts using real-life evidence from naturally acquired infection. Our findings can thus inform guidance as to how to safely end self-isolation."

She further added, "If you test positive for COVID-19 or have symptoms after being in contact with someone with confirmed COVID-19, you should try to stay home and minimise contact with other people."

Most participants in the study were white, middle-aged, had a healthy BMI, and had no medical conditions. In other age groups and in those with medical conditions, these results may vary as they may be slower at clearing the virus.

A person's infectiousness is one factor involved in the transmission, alongside behavioural and environmental factors, such as where people are mixing, and if they are in close proximity to one another.

The study was funded by the National Institute for Health and Care Research.

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