Boris Johnson is still resisting calls to reduce the isolation period for positive Covid cases from seven days down to just five.

The pressure is growing after the US made a dramatic change to its rules this week, having previously ordered those infected with Covid to isolate for 10 days.

Now asymptomatic Americans who tested positive can walk away after five days of isolation, but must continue to mask up for a further five days if they have not received their booster jab.

They do not have to test negative before leaving isolation.

At the moment, vaccinated and unvaccinated people in the UK can leave isolation only if they receive a negative result on a lateral flow test on both day six and day seven of their self-isolation, while unvaccinated people do still have isolate for 10 days if they have been a close contact of a positive case in the UK.

So why do people want to change the rules again?

• It would enable more NHS staff to work, strengthening the UK’s frontline against the virus.

• Approximately 40% of London’s NHS workers are currently in isolation, according to doctors.

• Up to 800,000 people are thought to be in isolation across the country at the moment, according to The Times.

• All public services, including bin collections and rail services, have been hit by staff shortages, so reducing the isolation period would benefit a range of industries.

• Omicron is highly transmissible, but appears to trigger less severe symptoms.

• The US centres for Disease Control and Prevention said its new measures will “ensure people can safely continue their daily lives”. It also claims that most people’s viral load drops off significantly after five days, making them less likely to be infectious.

• Professor of medicine at the University of East Anglia, Paul Hunter, told the BBC that Covid needs to become “effectively just another cause of the common cold” and so the isolation period needs to be reduced further. He wants five-day isolation periods where people could be released when they tested negative on a lateral flow test.

• Theresa Villiers, a former cabinet secretary, is also pushing to reduce the isolation period. She told The Daily Mail: “With encouraging data on Omicron…we need some pragmatism to ensure there isn’t another pingdemic.”

• Professor Tim Spector from King’s College London’s Zoe Covid app also backed reducing the isolation period to just five days to “protect the economy”.

• Johnson already reduced the isolation period from 10 days to seven last week, and the effects remain to be seen.

• The minister for disabled people Chloe Smith also told Times Radio that Downing Street is waiting to see how this goes, and that “we don’t have current plans to change from seven days”.

• The UK Health Security Agency advised the government to cut the isolation period to just seven days, but it is has not yet recommended any further reductions.

• Virologist at Warwick Medical School, Professor Lawrence Young, endorsed Britain’s current strategy and told The Guardian: “The approach adopted in the UK is sensible based on seven days and two consecutive negative lateral flow tests. These tests are a great way to determine if you are infectious.”

• Professor of respiratory sciences, Dr Julian Tang from the University of Leicester, also said the US decision to make positive cases wear masks for five days after their isolation ends would only be effective if masks were worn conscientiously.

• The government is already struggling to supply the country with enough lateral flow tests and PCR tests. Reducing the isolation period could therefore cause further problems.

• Elsewhere in Europe, the self-isolation period remains much longer. In Germany, it is a full 14 days unless a PCR test comes back negative, or a local health office permits release. In France, positive cases have to isolate for 10 days.