Coronavirus vaccines are being rolled out to millions of people across the UK, as all four nations are under lockdown measures to try to restrict the spread of the disease.

Here the PA news agency looks at how the country is going to come out of lockdown and how quickly vaccine distribution could help left restrictions.

– Why has another lockdown been introduced in England?

In a televised address on Monday evening, Prime Minister Boris Johnson said hospitals were under more pressure than at any time since the start of the pandemic, with the number of Covid-19 patients in hospital in England rising by nearly a third in the last week to 27,000.

Mr Johnson said that with record cases across the UK and deaths up by 20% over the last week, England needed to enter a new national lockdown.

– When will the lockdown end?

It is not clear yet how long the lockdown will last, but the Prime Minister said the “prospect” of the vaccination programme being rolled out across the country could enable restrictions to be progressively eased from mid-February when the most vulnerable are protected.

He told reporters on Tuesday: “When a very considerable proportion of the most vulnerable groups have been vaccinated … then there really is the prospect of beginning the relaxation of some of these measures.

“But you will also appreciate there are a lot of caveats, a lot of ifs built into that, the most important of which is that we all now follow the guidance.”

In a round of broadcast interviews earlier on Tuesday, Mr Gove said relaxation of the rules may have to wait until March – and that even then some measures may have to remain in place.

– How fast is the virus spreading?

The latest figures showed a further 830 people have died within 28 days of testing positive for Covid-19 as of Tuesday, and there were a record 60,916 more lab-confirmed cases of coronavirus in the UK.

It brings the total number of cases in the UK to 2,774,479 and the total deaths to 76,305.

According to ONS figures, one in 50 people in private households in England had the virus between December 27 and January 2, which rose to one in 30 in London.

– At what stage is the vaccine rollout?

The first Oxford/Astra Zeneca jabs were rolled out from Monday, joining the Pfizer medicine which was first made available in December.

Speaking from Downing Street on Tuesday evening, Mr Johnson said that 1.3 million people in the UK – including 1.1 million in England – have now received the coronavirus vaccine.

The Prime Minister told a No 10 press conference the figures include 650,000 people over the age of 80 – 23% of all the over-80s in England.

“That means nearly one in four of the most vulnerable groups will have in two to three weeks a significant degree of immunity,” he said.

“That is why I believe the Joint Committee on Vaccination and Immunisation was right to draw up a programme saving the most lives the fastest.”

Top of the priority list are people who live and work in care homes, followed by people over the age of 80 and frontline health and social care workers, including NHS staff.

Next on the list are people over the age of 75, and the fourth group are people aged 70 and those classed as clinically extremely vulnerable.

– How quickly will the vaccines be distributed from here?

Mr Gove said the NHS was working “24/7” to ensure 13 million people in the top four groups are offered a vaccine by the middle of February.

Chief medical officer Professor Chris Whitty called this timetable “realistic but not easy”.

He told a No 10 press briefing: “The NHS is going to have to use multiple channels to get this out but they are very determined to do this, but that does not make it easy.

“And, of course, in the case of the Pfizer vaccine, as I think is widely reported, it’s more difficult to handle because of the complicated cold chain model.

“We also, with both vaccines, wanted to be very careful in the first two or three days that we went a little bit slowly just in case there were some initial unexpected problems.”

Prof Whitty also said that extending the gap between the first and second jabs would mean the number of people vaccinated can be doubled over three months.

He explained: “If over that period there is more than 50% protection then you have actually won. More people will have been protected than would have been otherwise.

“Our quite strong view is that protection is likely to be lot more than 50%.”

– Could the virus mutate and render vaccines ineffective?

Sir Patrick Vallance said it is possible the South African coronavirus variant may have some impact on vaccine effectiveness but is unlikely to “abolish” their effect.

The chief scientific adviser told the Downing Street press conference that a possible change in the virus shape in the variant “theoretically gives it a bit more risk of not being recognised” by the immune system.

“There is nothing yet to suggest that’s the case. This is being looked at very actively,” he said.

“It’s worth remembering that when a vaccine is given you don’t just make one antibody against one bit, you make lots of antibodies against lots of different bits, and so it’s unlikely that all of that will be escaped by any mutations.

“But we don’t know yet.

“At the moment, you’d say the most likely thing is that this wouldn’t abolish vaccine effect. It may have some overall effect on efficacy but we don’t know.”

– Are there other factors involved in deciding whether the lockdown can be lifted?

Throughout the pandemic there have been a whole host of factors used to decide whether to impose or relax restrictions.

One of the key ones has been the virus’ reproductive number, or R value, which is the rate the virus is spreading. If the R number is above one, it means the infection is growing.

Sage member Professor Calum Semple said the R rate on the downslope was not a very useful indicator and what needed to come down were case numbers presenting to hospital and levels of sickness within the community.

Other factors which have previously been considered include case rates, rates in the over-60s, the positivity rate – the number of positive cases detected as a percentage of tests taken – and the pressure on the NHS.

It is not clear which of these factors, or any others, will also be considered when the Government comes to decide whether to ease restrictions.