The five full days from seven are reduced from next Monday in England to the minimum isolation time for those who are fully vaccinated and are diagnosed positive for coronavirus.
Those who take two negative rapid tests, on the fifth and the morning of the sixth day, will be able to leave the quarantine immediately after.
The government had reduced the quarantine time from ten to seven days last month.
Announcing in the House of Commons, Health Minister Sajid Javid cited studies by the UK Health Insurance Agency showing that two-thirds of the carriers of the virus are no longer contagious by the end of the fifth day.
Mr Javid said the move "would maximize activity in the economy and education".
The minister also said that about 17.000 coronavirus carriers are currently being treated, warning that the NHS health system will remain under "significant pressure" for the coming weeks. However, he noted that it was "encouraging that we have not seen an increase in patients in intensive care units", and that there are indications of a decrease in the rate of increase in hospitalizations.
Omicron is a milder mutation in the severity of the infection, Javid added, but it still needs caution, as a significant number of carriers could still end up in hospital, especially if they are not vaccinated.
According to the Minister, the country's defense against Omicron is fully strengthened by vaccinations, the plethora of diagnostic tests and antiviral drugs available.
He also confirmed that it would be mandatory for NHS front-line workers to be fully vaccinated by 1 April. The proportion of NHS workers who have taken the first installment has risen from 92% to 94% since the announcement of their vaccination obligation for health workers.
