The coronavirus crisis could be as serious and deadly as the 1918 flu pandemic which killed up to 50m people around the world, a former CDC infectious disease specialist has warned.

As health experts from Milan to Wuhan scrambled to try and stop the spread of Covid-19, which has now infected more than 108,000 people and killed 3,800, an epidemiologist in Washington state has warned that “people you know” will likely die.

“It’s possible that COVID-19 will be similar to a bad flu year but there are a number of indications that it will be very much like the 1918 flu pandemic,” wrote Juliana Grant, a preventive medicine physician and infectious disease epidemiologist. “To put that in perspective, the 1918 flu did not end civilisation as we know it but it was the second-deadliest event of the last 200 years. It is likely that people you know will die from Covid-19.”

Ms Grant’s comments came as officials in Washington state, the epicentre of the crisis in the US, declared three new deaths had been reported, bringing the total to 20 in the state and perhaps 24 nationally.

Donald Trump, who has been accused of playing down the threat posed by the disease, tweeted: “So last year 37,000 Americans died from the common flu. It averages between 27,000 and 70,000 per year. Nothing is shut down, life & the economy go on. At this moment there are 546 confirmed cases of coronavirus, with 22 deaths. Think about that!”

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Ms Grant made her comments about the 1918 flu on her personal blog and was not immediately available to comment further.

In her post, she wrote: “There is one critical difference between Covid-19 and the 1918 flu – the 1918 flu virus hit children and young adults particularly hard. Covid-19 seems to be most severe in older adults. Children and young adults generally have mild infections and we are grateful for this.”

In a separate post about why she made the comparison with the events of a century ago, she said she was struck by both the transmission rate and mortality rate.

“The early reports of Covid-19 are showing a mortality rate of 1.5 – 3 per cent meaning that 1.5-3 per cent of people who are infected die. This is approximately 10-30 times higher than the mortality associated with seasonal flu in the US and in the same general vicinity as 1918 flu,” she said.

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“Early reports indicate that each person with Covid-19 infection gives the virus to more than two other people (on average). This is referred to as the transmission rate.”

She added: “We think the transmission rate for seasonal flu is less than two but the 1918 flu transmission rate is about the same as what we’re seeing with Covid-19. Again, these are estimates and we don’t yet know if they are correct.”

Peter Hotez, dean of tropical medicine at Baylor College of Medicine, in Houston, has urged Congress not to minimise the virus’ risk for vulnerable or people.

He testified on Capitol Hill it was “like the angel of death for older individuals”.

Mr Hotez told The Independent he was deeply concerned some people were not taking seriously enough the risk to places such as care homes such as the one in Kirkland, near Seattle, where most of the deaths in the US have occurred.

Asked about Ms Grant’s comparison to the 1918 flu pandemic, he pointed out – as she did – that young people do not currently appear at risk from the coronavirus

“What worries me about this virus is this: it is not the deadliest virus we’re ever seen, especially compared to something like Ebola. Nor is it the most transmissible disease we have seen,” he said.