Wuhan virus: Experts fear tens of thousands may be hit

WASHINGTON/BEIJING • The deadly coronavirus outbreak in China will afflict tens of thousands of people at a minimum and last at least several months, researchers estimate based on the first available data.

"The best case scenario, you would have something... where we go through the spring into the summer, and then it dies down," said Dr David Fisman, a professor at the University of Toronto, who wrote an analysis of the virus for the International Society for Infectious Diseases.

Another expert, Northeastern University professor Alessandro Vespignani, said: "It's not something that's going to end the next week or the next month."

Epidemiologists have only piecemeal information on the new 2019-nCoV virus which appeared last month in the Chinese city of Wuhan. They use mathematical models to estimate the actual number of cases, as of the current date, and compare them with past outbreaks - but many of their hypotheses remain uncertain.

Until the past weekend, researchers thought that infected people were not contagious until they began exhibiting symptoms, such as fever, respiratory problems and pneumonia. But the Chinese authorities said on Sunday that they had established the opposite.

The US health authorities said on Monday that they had not seen evidence that asymptomatic patients can infect other people. But if they can, this would definitely change the outbreak's dynamics.

The first estimates for the length of the incubation period - about two weeks - are recent. In recent days, multiple experts have calculated an important parameter for any outbreak: the basic reproduction number, or R0. It represents the number of people contaminated by an infected person.

Estimates range from 1.4 to 3.8, according to Dr Fisman, figures that are considered moderate. That is only an average: Some patients may infect many people, while others infect only a few.

"On its own, it isn't a reason to panic," said researcher Maimuna Majumder of Harvard University and Boston Children's Hospital. She said the rate is 1.3 for seasonal flu and between two and five for the severe acute respiratory syndrome (Sars), which resulted in 8,000 cases and 774 deaths in 2002 to 2003. In comparison, the rate for measles ranges from 12 to 18.

Quarantines and isolation measures, systematic hand washing and masks could help drive down the average number of infected people. If the rate falls below one, the epidemic will die down.

The effect of the control measures by China will not be felt for another week or two, researchers say.

"The more we learn about it, the more it looks like Sars," said Dr Fisman. "Sars was controllable; hopefully this will be too... It's going to be many weeks, probably months, and nobody knows where this will go."

The US health authorities said on Monday that they have sequenced the genome of the first two cases reported in the country and confirmed it has not mutated since leaving China.

"All the sequences we've extracted are similar to the one that China initially posted a couple of weeks ago," said Dr Nancy Messonnier, head of respiratory diseases at the Centres for Disease Control and Prevention (CDC).

She was planning imminent changes on measures to control and track the deadly virus, beyond the current restrictions just on travellers arriving from Wuhan. All passengers from Wuhan are currently subject to testing in 20 US airports.

China has announced that people who are infected can spread the disease before they show any symptoms. That has rendered redundant the current measures to contain the virus in the US.

Despite that, the CDC still estimates the risk from the virus to be low, said Dr Messonnier.

Meanwhile, an expert at China's National Health Commission said yesterday that one week is sufficient for a recovery from mild coronavirus symptoms.

Dr Li Xingwang also said mild symptoms do not present as pneumonia, but just slight fever.

AGENCE FRANCE-PRESSE, REUTERS