Daily testing for anyone double-jabbed who comes into contact with a COVID-19 case will start from Tuesday.
Those fully vaccinated should take a daily lateral flow test for seven days to slow the spread of the virus, the government has said.
Unvaccinated adults must continue to self-isolate for 10 days if they are a contact of someone with COVID, and anyone who tests positive or develops symptoms will need to self-isolate.
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People will be contacted by NHS Test and Trace or via the NHS COVID-19 app to tell them they are a contact of someone who tested positive and what action they need to take.
The move comes following a significant rise in Omicron infections in the UK with the variant expected to become the dominant strain in the UK by mid-December.
Health Secretary Sajid Javid said: “We are taking this proportionate and more practical measure to limit the impact on people’s day to day lives while helping to reduce the spread of Omicron.
“Vaccines remain our best defence and I urge anyone yet to get a first and second jab to come forward and those eligible for a booster to get boosted as soon as possible.”
Dr Jenny Harries, chief executive of the UK Health Security Agency, said: “If you are identified as a contact of someone with COVID-19, taking a rapid daily test – and only needing to isolate if it is positive – will help reduce the spread of the virus and minimise its impact on our everyday lives over the coming weeks and months.”
“Rapid tests are freely available in pharmacies and online.
“Our latest analysis shows that boosters provide the best protection against the Omicron variant, please go forward when you are called.
“If you haven’t had any vaccine, a first and second dose still gives you protection against becoming seriously unwell. Don’t worry about stepping forwards now – you will be warmly welcomed by our vaccination staff and I would strongly advise you to get vaccinated as soon as possible.”