Persistent Covid infections in immuno-compromised patients can result in new variants which may be more difficult to combat, a team of Amsterdam UMC researchers had warned.

Doctors discovered that the Omikron variant of the virus had mutated 50 times while inside the body of one patient who was 72 years old and suffering from underlying illnesses.  He became infected in 2022, was hospitalised and continued to test positive for the virus until he died 613 days later.

Doctors said that as far as they could tell, the man did not infect others with the mutated virus.

The case, which will be presented at a medical conference in Barcelona at the end of the month, is important because it sheds light on the behaviour of the virus in long-term infections.

There is, experts say, a risk that the mutated viruses are too strong for the immune systems of healthy people. “That would constitute a potential threat to public health”, one of the researchers said. Although rare, cases such as this merit more research, he said.

Public health institute RIVM classifies the current spread of Covid as “low”, with an average of 49 hospitalisations per week.