As Chinese authorities widened a massive urban lockdown and flew large numbers of medical personnel to Wuhan, the epicentre of a new SARS-like virus, medical authorities provided new indications that weeks of inaction had allowed the virus to spread widely before serious measures were taken.

Chinese authorities initially reported that the new 2019-nCoV coronavirus had most seriously affected the elderly and those left vulnerable by pre-existing health conditions.

But an academic study published by Chinese researchers in The Lancet on Friday found that of the first 41 confirmed cases of the virus, which causes pneumonia-like symptoms, “less than half had underlying diseases.” Nearly half were 49 years of age or younger. And a third had not been exposed to the wild animal market identified as the source of virus, suggesting that even from the earliest days, it had begun to leap between people.

Fifteen per cent of those first 41 people died.

“We are concerned that 2019-nCoV could have acquired the ability for efficient human transmission,” warned the paper’s authors, who included dozens of doctors from hospitals in Wuhan and major state institutes for infectious disease research.

The first of the patients was admitted to hospital on Dec. 16, more than a month before Chinese authorities began to lock down Wuhan and neighbouring cities in Hubei province.

By Saturday evening, nearly all of Hubei, with a population of 58 million, was under some form of lockdown, with authorities halting most forms of transportation and barring entry and exit to at least 15 cities. China has counted 1,369 confirmed cases and 41 deaths. New cases have also been confirmed in Malaysia, Australia, Nepal, France, Singapore and the U.S.

Now, new evidence is emerging that officials in Wuhan deliberately downplayed the virus, even after formally notifying the World Health Organization on Dec. 31 about what the WHO described as “a cluster of cases of pneumonia of unknown cause.”

But the Wuhan government took a “refrigerating strategy” in the early days of the viral spread, a doctor at Wuhan Union Hospital told China News Weekly. Medical staff were banned from speaking publicly about what was taking place or accepting media interviews, the doctor said.