A man living in the United States has contracted coronavirus twice, with doctors reporting the second infection becoming far more dangerous than the first.
The 25 year old was left needing hospital treatment after being unable to breathe properly. He has now recovered.
No known health problems
The man, who is from Nevada, had no known health problems or immune defects that would make him particularly vulnerable to Covid-19.
Originally contracting the virus on 18 April, the man’s initial symptoms were fully resolved by 27 April.
He had two further tests for coronavirus on 9 and 26 May, and tested negative for the virus both times. However, on 28 May he developed symptoms again, including a fever, headache, dizziness, cough, nausea and diarrhoea.
On 5 June, he tested positive for coronavirus for the second time, with scientists saying he caught the virus twice, rather than the original infection becoming dormant and then bouncing back.
Dr Mark Pandori, from the University of Nevada said, “Our findings signal that a previous infection may not necessarily protect against future infection,
“The possibility of reinfections could have significant implications for our understanding of Covid-19 immunity."
Dr Pandori advised that people who have recovered from the virus should continue to follow guidelines around social distancing, face masks and hand washing.
Reinfection seems to be rare
So far, globally, there have only been a few cases of reinfection out of the 37 million confirmed cases of Covid-19.
Scientists in Hong Kong recently reported on the case of a young man who recovered from a bout of Covid-19 only to be re-infected more than four months later. The scientists proved it was two different strains of the virus using genome sequencing.
Experts say re-infection isn’t surprising, but is likely to be rare, with large studies needed to understand why this might happen.
Scientists had originally assumed that a second round of Covid-19 would be milder, as the body would have learned to fight the virus the first time around.
The latest study in the Lancet Infectious Diseases poses a question as to why the Nevada patient became more severely ill the second time. One idea is that he may have been exposed to a bigger dose of the virus.
Professor Paul Hunter, from the University of East Anglia, said the study was "very concerning" because of the small gap between the two infections, and the severity of the second.
How long does immunity last?
The immune system has a memory like our own, and will remember infections clearly, but will forget others over time.
Covid-19 has not been around long enough to know how long immunity might last, but there are six other human coronaviruses that can give a clue.
Four of those produce the symptoms of the common cold and immunity is short lived. Studies have shown that some patients could be re-infected within a year.
Immunity is important because it will determine whether you will get Covid-19 multiple times and how often.
Immunity will also affect how deadly the virus is. Understanding immunity could help ease lockdown if it is clear who is not at risk of catching or spreading the virus.