The coronavirus has mutated into at least two separate strains since the outbreak began in December, according to Chinese scientists.
Researchers say there are now two types of the same coronavirus infecting people – and most people seem to have caught the most aggressive form of it.
At least 94,000 people have been infected around the world and almost 3,200 have died, while 50,000 have recovered from the disease.
The team of experts from Beijing and Shanghai said 70 per cent of people have caught the most aggressive strain of the virus but that this causes such bad illness that it has struggled to spread since early January.
Now an older, milder strain seems to be becoming more common.
Knowing that the virus can mutate may make it harder to keep track of or to treat, and raises the prospect that recovered patients could become reinfected.
The experts cautioned that the study that discovered the mutation only used a tiny amount of data – 103 samples – so more research is needed, and another scientist added that it is normal for viruses to change when they jump from animals to humans.