Experts are examining whether the period could be cut from seven to five days for cases, something which would help ease staffing crises across the economy and public services.
Mr Johnson also pledged free lateral flow tests would be available for “as long as it is necessary” as ministers considered how to move to a position of living with Covid-19.
The Prime Minister said testing was an important line of defence, along with vaccinations, in the face of the Omicron wave.
Mr Johnson is under pressure from Tory MPs to commit to ending restrictions and shift to a position where Covid-19 is treated in a similar way to other illnesses which do not require state interventions.
There is also a debate in Cabinet about cutting the self-isolation period, as the United States has done.
Chancellor Rishi Sunak is among ministers keen on the economic benefits of reducing the period from seven to five days, according to the Daily Telegraph, while UK education secretary Nadhim Zahawi has suggested the move could help ease staffing problems.
Asked about the issue on a visit to a vaccine clinic at a pharmacy in his Uxbridge constituency, Mr Johnson said: “The thing to do is to look at the science. We are looking at that and we will act according to the science.”
Following reports the supply of free lateral flow devices will end as part of the Government’s plan to live with Covid, Mr Johnson said: “We are going to have to make sure we continue to use testing as one of our most important lines of defence for as long as is necessary.”
Around 100,000 critical workers were beginning to be offered daily lateral flow testing to help spot and isolate asymptomatic cases and limit the risk of outbreaks in key workplaces.
A further 141,472 cases were announced on Sunday, the fifth consecutive fall. However, this number should be treated with caution as reports often drop on the weekend.
The most recent UK-wide figures from January 6 showed 18,454 people were in hospital with Covid-19, with 868 requiring ventilation.
Mr Johnson acknowledged the NHS was “still under a lot of pressure” and stressed the need for people who have yet to receive a booster jab “to join the movement”.
Meanwhile Cabinet minister Michael Gove said the country was moving to a stage where it can “live with Covid”.
Mr Gove acknowledged there would still be “difficult weeks ahead” with the NHS facing real pressure, and it was not yet possible to say the current Omicron-driven wave of Covid-19 cases was abating.
The Levelling Up secretary, who was one of the voices around the Cabinet table arguing for tougher measures when Omicron emerged, said the easing of restrictions would have to be guided by science, but “the sooner the better”.
He told Sky News: “We are moving to a situation, we’re not there yet, but we are moving to a situation where it is possible to say that we can live with Covid, and that the pressure on the NHS and on vital public services is abating.”
But after the current “difficult period”, Mr Gove told BBC Radio 4’s Today he hopes “there will be better times ahead”.
“There are other coronaviruses which are endemic and with which we live, viruses tend to develop in a way whereby they become less harmful, but more widespread,” he said.
“So, guided by the science, we can look to the progressive lifting of restrictions and, I think for all of us, the sooner, the better.”
The current Plan B measures in England, including guidance to work from home where possible and the widespread use of face coverings, are set to be reviewed on January 26.
Former Tory chief whip Mark Harper, leader of the Covid Recovery Group of Conservatives, warned if Mr Johnson sought to extend the measures, he could face a revolt even larger than the 100 Conservatives who defied him when they were first introduced in December.
Mr Harper said: “The Prime Minister sort of wants to agree with us on the backbenches, that we have to be realistic about living with Covid forever… then he says he wants to keep restrictions in reserve or won’t rule them out.
“This is becoming an unsustainable position.”
Clive Watson, chairman of the City Pub Group, told BBC Radio 4’s Today programme things had been “really, really tough for the hospitality industry”, adding: “Why do people who work in hospitals or work in retail go to work, but office workers are exempted from going to work?”
Professor Graham Medley, a member of the Government’s Scientific Advisory Group for Emergencies (Sage) panel, said the shift towards living with Covid-19 would be a phased transition.
“It can’t be an emergency forever,” he told BBC Radio 4’s Today.
“So at some point it will have to stop being an emergency but that is likely to be a phase out rather than an active point in time where somebody can declare the epidemic over.”
Dr David Nabarro, the World Health Organisation’s special envoy on Covid-19, told Sky News: “I’m afraid we are moving through the marathon, but there’s no actual way to say that we’re at the end – we can see the end in sight, but we’re not there.
“And there’s going to be some bumps before we get there.”