Can you get Covid-19 twice or does it cause immunity?

President Trump tweeted that he could no longer get Covid-19 after testing positive during the election campaign

The number of cases of coronavirus has reached more than 99.7m globally, as the pandemic continues its spread around the world.

The UK is approaching 100,000 deaths while the USA has surpassed 400,000 dead. However, the figures also show that hundreds of thousands of people have recovered from the disease.

Once you’ve had the illness are you able to catch it again? Former President Trump was one of those who claimed that he is “immune” after testing positive for the virus on 1 October and subsequently recovering.

The president tweeted: "A total and complete sign off from White House Doctors yesterday. That means I can’t get it (immune), and can’t give it. Very nice to know!!!” The tweet was later flagged by Twitter as “spreading misleading and potentially harmful information”.

So can you get coronavirus twice? This is what you need to know about coronavirus immunity and contracting the virus more than once.

If you recover from the new coronavirus, do you have immunity? 

To date, there have been more than two million deaths from coronavirus globally. However, most people infected with Covid-19 virus have mild disease and recover, according to the World Health Organisation (WHO) .

But, just because you recover from the virus does not mean you cannot catch it again, WHO confirmed in a statement released on 24 April.

"There is currently no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection," the organisation said.

According to Li QinGyuan, director of pneumonia prevention and treatment at China Japan Friendship Hospital in Beijing, those who have been infected with Covid-19 develop a protective antibody - but it isn’t clear how long the protection lasts.

"However, in certain individuals, the antibody cannot last that long," Li told USAToday. "For many patients who have been cured, there is a likelihood of relapse."

In children, it is currently believed that the virus causes the development of “at least short-term immunity”.

“No one knows for sure, but most children likely develop at least short-term immunity to the specific coronavirus that causes Covid-19,” Dr Peter Jung, an assistant professor of pediatrics at the University of Texas Medical School at Houston told The Huffington Post. “But just as the flu can mutate, so could Covid-19, which would make an individual susceptible to reacquiring the infection.”

According to an August study, researchers have identified a 25-year-old man in the United States who was reinfected with the virus. 

In the report, it states that the man tested positive for the virus in April, at which point he showed mild symptoms. He later tested positive again in May and developed more serious symptoms of Covid-19.

In a statement to Reuters, Kristian Anderson, professor of immunology and microbiology at Scripps Research in La Jolla, California, said: “This study likely represents a clear example of reinfection ... reinfections are possible - which we already knew, because immunity is never 100 per cent.”

According to the researchers, they were able to identify that the man’s seperate infections “represented genetically different strains" of the virus. 

However, the researchers did note that reinfection is probably rare, but that more research needs to be done to know for sure whether the virus causes immunity. 

Previously, it was thought that people who initially recovered were more likely to relapse rather than get reinfected with the virus.

According to one study, people with mild infections can test positive for the virus by throat swabs “for days and even weeks after their illness”.

But, that doesn’t mean it isn’t possible to contract the disease again, especially in those who are immunocompromised.

“The immune response to Covid-19 is not yet understood,” the Centers for Disease Control and Prevention (CDC) explains. “Patients with MERS-CoV infection are unlikely to be reinfected shortly after they recover, but it is not yet known whether similar immune protection will be observed for patients with Covid-19.”

And, as WHO states, "As of 24 April 2020, no study has evaluated whether the presence of antibodies to SARS-CoV-2 confers immunity to subsequent infection by this virus in humans."

While further studies are needed to understand whether it is likely for an individual to be reinfected with new coronavirus, experts recommend those who have been infected follow the hygiene steps outlined by CDC, which include staying away from people who are sick, frequently washing hands, and covering coughs and sneezes.