Boris Johnson’s role as prime minister has been impacted by Covid-19 for the second time, after he was forced into self-isolation on the night of Sunday 15 November.

A Tory MP, who Mr Johnson was in contact with during a Downing Street meeting, tested positive for the virus.

The Prime Minister, who said he does not have symptoms, along with three other MPs will now have to self-isolate for 10 days during what has been said to be a crucial week for the government.

Boris Johnson is self-isolating for the second time after coming in contact with an MP who tested positive (PA Media)

It comes a few months after Mr Johnson contracted coronavirus in March and was self-isolating in Downing Street, before his condition worsened and he was moved to intensive care.

So, why is the Prime Minister isolating again and is he immune from the virus after previously becoming infected?

Why is Boris Johnson isolating again?

Lee Anderson, the Conservative MP for Ashfield, Nottinghamshire, tested positive for coronavirus after he attended a 35-minute meeting between a group of MPs and the Prime Minister.

On Friday 13 November, the day after the meeting, Mr Anderson lost his sense of taste - one of the key coronavirus symptoms.

As well as the Prime Minister, three more Tory MPs are isolating following the meeting - Lia Nici of Great Grimsby, Brendan Clarke-Smith of Bassetlaw and Warrington South’s Andy Carter.

Boris Johnson was pictured standing next to Mr Anderson inside Downing Street on Thursday 12 November. They appear to be standing at a distance but neither men are wearing masks.

Downing Street said it was a Covid-secure workplace, and that Mr Johnson had been told by NHS Test and Trace to self-isolate as a precaution due to the length of the meeting.

Boris Johnson is said to have had contact with other people since the initial meeting, including top aides Dominic Cummings and Lee Cain before both of them left Downing Street for good following a “power struggle”.

Will Boris Johnson still carry out his duties at Downing Street?

As well as trying to restore calm to No 10 after the in-fighting between his inner circle, Boris Johnson faces an important week as Brexit negotiations with the EU reach the final stage.

Downing Street said he would still make public statements and continue to carry out his ministerial duties, including chairing Covid meetings.

There are talks of Mr Johnson participating in House of Commons proceedings remotely.

A No 10 spokesperson said: “The Prime Minister will follow the rules and is self-isolating. He will carry on working from Downing Street, including on leading the government’s response to the coronavirus pandemic. The PM is well and does not have any symptoms of Covid-19.”

Is Boris Johnson immune to coronavirus?

The Prime Minister took to Twitter on Monday 16 November to tell followers via a video clip that he is feeling “great”.

He said he is “in good health” and experiencing no coronavirus symptoms, claiming he is “bursting with antibodies” after his first infection seven months ago.

Mr Johson added: "The good news is that NHS Test and Trace is working ever-more efficiently, but the bad news is that they've pinged me and I've got to self-isolate because someone I was in contact with a few days ago has developed Covid.

"It doesn't matter that we were all doing social distancing, it doesn't matter that I'm fit as a butcher's dog, feel great.

"And actually, it doesn't matter that I've had the disease and I'm bursting with antibodies. We've got to interrupt the spread of the disease and one of the ways we can do that now is by self-isolating for 14 days when contacted by Test and Trace."

Scientists are still trying to figure out whether having coronavirus impacts a person’s immunity to the virus.

It is thought that the sickest patients develop the strongest immune response to Covid-19 - so given that Boris Johnson spent several days in intensive care, he may be well-placed to fight off a future infection.

How long do Covid antibodies last?

Sars-CoV-2 hasn’t been around long enough for scientists to know exactly how long immunity lasts and whether everyone who has caught it becomes immune.

A study from King’s College London suggested that the antibodies that kill the virus deplete after three months.

Yet, the cells that manufacture antibodies - B cells - may remain even after antibodies disappear, meaning a second Covid infection would be milder than the first.

There were early reports of people appearing to catch the virus twice, but scientists put this down to errors in testing.

However, a man in the United States was reported in October to have caught Covid for a second time, with scientists concluding that a previous infection may not protect against future infection.

The incident raised questions about how much coronavirus immunity can be built up, although reinfections remain rare.

Is Boris Johnson immune to Covid? Why the prime minister is self-isolating and if he could catch coronavirus again