Scientists are calling for a return of a 10-day Covid-19 self-isolation period to protect the NHS from an expected winter surge.
A Lancet study has confirmed for the first time exactly how long we are infectious revealing two thirds of people who catch the virus are still contagious to some extent after five days.
Legally enforced self-isolation periods have now been scrapped and NHS guidance is currently to do so for just five days after testing positive.
That is despite infection rates still running relatively high with around one in every 25 people having it.
Cases are expected to surge as the summer ends, driving people indoors to socialise at a time when all pandemic restrictions such as mask wearing have been scrapped.
The new trial by Imperial College London carried out detailed testing analysis on 57 participants from the point they were exposed to the virus. It is the first to do so outside of a laboratory setting.
The average infectious period was five days and people were less contagious as time passed.
However one-quarter of participants were still infectious at day seven.
Study author Prof Ajit Lalvani, of 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 virus 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.”
Scientists are calling for a return of the requirement to record two negative lateral flow tests before leaving self isolation between days five and ten.
Such national guidance would need to place a duty on employers to allow staff to self isolate until it is safe for them to be released.
It would also require vast amounts of tests to be available to the public, possibly for free.
Professor Lalvani added: “Self-isolation is not necessary by law, but people who want to isolate need clear guidance on what to do.”
The findings are published in The Lancet Respiratory Medicine journal.
Current NHS guidance already recommends avoiding meeting people at higher risk from Covid-19 for 10 days after testing positive, even if they have been vaccinated.
Professor Susan Hopkins, Chief Medical Advisor at the UK Health Security Agency, said: “We know that most transmission in adults occurs three days before the onset of symptoms to five days after, and the infectiousness for Omicron peaks within a shorter time frame than previous variants.
“As we continue to live with Covid-19, it is clear that the vaccine programme is successfully keeping severe illness and deaths at a low level.
“We encourage everyone to make sure that they are up to date with all vaccines that they are eligible for. This remains our best defence against Covid-19.
“If you have symptoms of a respiratory infection, such as Covid-19, and you have a high temperature or do not feel well enough to go to work or carry out normal activities, try to stay at home and avoid contact with other people, until you no longer have a high temperature (if you had one) or until you no longer feel unwell.
“It is particularly important to avoid close contact with anyone who you know is at higher risk of becoming seriously unwell if they are infected with Covid-19 and other respiratory infections.
“UKHSA continues to monitor all available epidemiological, virological and genomic evidence in order to ensure that our guidance is appropriate. All of our guidance remains under constant review.”
