“Some common systemic symptoms of Covid-19 such as fever, fatigue, phlegm and muscle pain were more prominent in patients admitted before January 23, but more insidious in later patients.”

Patients who tested positive for the virus after January 23 did not experience these symptoms as much. There was a 50 per cent decrease in fever, 70 per cent decline in fatigue and an 80 per cent drop in muscle pain, according to the paper. Some of the 80 patients in the study could have been asymptomatic, it said.

According to the study, initial symptoms were milder after the lockdown was imposed, but there was no evidence that transmission or the pathogen had weakened. The doctors said the observations could be “characteristics of virus mutation”.

There has also been debate over the origins of the disease – whether or not it originated in China – and what genetic mutations could mean for prevention and control efforts.

A separate study by researchers from Peking University and the Chinese Academy of Sciences published on March 3 reached a similar conclusion on the effect of quarantines.

The newer virus strain accounted for 96 per cent of the samples collected in early January, suggesting it was more infectious, according to the study published in the National Science Review.

But that more aggressive strain was less prevalent in samples from China and other countries taken after the initial outbreak in Wuhan – falling to about 60 per cent of the total.

The researchers attributed that change in the virus to the mass quarantines. “These human intervention efforts might have caused severe selective pressure against the [aggressive] type,” they wrote in the paper.

China sends team of medical experts, gear to help Italy fight coronavirus

“If these changes are not due to sequencing errors, it would be interesting to test whether and how these mutations affect the transmission and pathogenesis of Sars-CoV-2,” they added, referring to the clinical name for the virus.

Another study led by Jiang Yongzhong from the Hubei Provincial Centre for Disease Control and Prevention also found that the virus had split into two major types, based on an analysis of 146 samples, according to a preprint paper on the bioRxiv website on March 4.

It also said the genetic make-up of the virus had changed after quarantine measures were imposed, and mutations had “occurred across the world … providing the possibility of widespread adaptation”.

Paul Young, head of the University of Queensland’s School of Chemistry and Molecular Biosciences, said the coronavirus would acquire new, random mutations as it spread.

“This is normal for a virus that contains an RNA genome [like Sars-CoV-2]. They naturally acquire mutations as they replicate,” he said.

“Most of these mutations, being random, have nothing to do with adaptation to the host and are simply a reflection of the high error rate in copying the viral genome.”

The European Centre for Disease Prevention and Control said comparing the data from patients in Italy to that of other places would provide a better understanding of the virus.

“Genomic information can support the identification of targets for treatment and vaccine development too, as well as the development of rapid diagnostic tests,” a spokesperson for the centre said. “In addition, by following the genomic changes over time, researchers can get the information on what happened to the virus in the past and foresee what can happen to it in the future.”

But others noted that the studies on the virus’ mutation were far from conclusive.

“The hospital observation in Wuhan, though valuable, must be treated with caution because it involved less than 100 patients,” said a doctor at a public hospital in Beijing treating virus patients who requested anonymity.

“Whether quarantine measures could have had such a big – and almost instant – impact on the evolution of the virus remains unclear.”

The Peking University-led study was more controversial, with researchers from the University of Glasgow asking Lu to withdraw the paper to avoid spreading “undue fear”. Lu responded that the researchers had misinterpreted his team’s conclusions.

But it would then have gone through hundreds of mutations before it became the virus that causes Covid-19, normally accumulating at a rate of one to two mutations a month. So the virus could have left the bat more than a decade ago, or it could have merged with new genes on an unknown intermediate host.

According to Wu Yonghua, a scientist at Northeast Normal University in Changchun, the new coronavirus could be just the latest in an army of diseases to come.

Wu has studied the evolution of the new strain, as well as Sars – which is also believed to have jumped from bats to another animal – and more than 30 other coronaviruses found in bats.

At least 10 of them were evolving on paths that could eventually mirror the same course as the new coronavirus and Sars, developing the same protein spike that would allow it to effectively bind with human cells, according to Wu’s preprint paper on bioRxiv on March 5.

“[They] may be potential novel coronaviruses that will infect humans in the future,” he said.

Additional reporting by Keegan Elmer