The new strain of coronavirus continues to spread across the UK, with cases rising exponentially.
On Tuesday 29 December, 53,135 new cases were recorded, with Health Secretary Matt Hancock saying the NHS was facing “unprecedented pressures”.
The rapid spread of the new variant - thought to be up to 70 per cent more transmissible - has caused concerns about whether it is possible to catch coronavirus for a second time.
Here’s what we know so far about getting Covid twice - and how immunity works.
Can you catch coronavirus twice?
Health experts believe that those who have caught coronavirus once could still become infected again.
The World Health Organisation (WHO) confirmed in a statement back in April that reinfection from coronavirus could be possible: "There is currently no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection.”
However, a study of the new strain carried out by Public Health England found that the mutations do not mean it is more likely that people will be reinfected.
Only two reinfections in the variant group were found, at least 90 days after the first infection.
Susan Hopkins, senior medical adviser to Public Health England, said investigations would be continuing to understand the new strain better.
At the start of the pandemic, there were early reports of people appearing to have multiple coronavirus infections in a short timeframe, but scientists have since said this was down to inaccurate testing.
Reinfections are also still rare, with only a few hundred cases reported globally.
In mid-October, Mexico said it had recorded 258 reinfection cases.
The same month, an 89-year-old Dutch woman was the first documented death of a patient who had caught the virus twice, while in November Sweden launched an investigation into 150 cases.
Scientists in Hong Kong also recently reported the case of a young, healthy man who recovered from Covid-19 but was reinfected more than four months later.
Identifying reinfection is also difficult, as the coronavirus can linger in the body.
Currently, no human has been deliberately reinfected with coronavirus to test immunity - but two macaque monkeys have been.
In the test, the monkeys were infected twice, firstly to build up an immune response and then a second time three weeks later.
The experiment showed that the monkeys did not develop symptoms again after a quick reinfection.
How do you become immune to coronavirus?
Your body relies on its adaptive immune response to fight off the coronavirus, which includes the cells that produce the antibodies that stick to the virus to stop it attacking.
Studies have shown that it takes roughly 10 days for your immune system to start making antibodies to target Covid-19.
It is also believed to be the sickest patients who develop the strongest immune response to the virus.
Whether those who only have mild symptoms or are asymptomatic have a strong immune response is yet unknown.
If your adaptive immune response is powerful, it could leave a lasting memory of the virus which could protect against reinfection.
Yet, the immune system is able to remember some infections well, like measles, but can also forget others.
How long does immunity last?
Immunity to Covid-19 may reduce over time, just like it does with other illnesses.
This specific coronavirus has not yet been around long enough for scientists to understand exactly how long immunity lasts.
However, studies of other coronaviruses that infect humans have shown immunity does not last for long, and patients could be reinfected within 12 months.
Researchers from King’s College London also found that the levels of antibodies needed to stop coronavirus reduced over three months.
Yet, even if antibodies wane, the B cells that manufacture them could stick around in the body, meaning a second infection of coronavirus would be milder than the first one.
Even if you do have antibodies from coronavirus, immunity is not guaranteed - so there is the possibility that you could still catch the virus and pass it on to others.