A piece of research that helped convince the British government to impose more stringent measures to contain COVID-19 painted a worst case picture of hundreds of thousands of deaths and a health service overwhelmed with severely sick patients.
In a sharp toughening of Britain's approach to the outbreak on Monday, Prime Minister Boris Johnson closed down social life in the world's fifth largest economy and advised those over 70 with underlying health problems to isolate.
The projection study, by a team led by Neil Ferguson, a professor of mathematical biology at Imperial College London, used new data gathered from Italy, where the infectious disease epidemic has surged in recent weeks.
Comparing the potential impact of the COVID-19 disease epidemic with the devastating flu outbreak of 1918, Ferguson's team said that with no mitigating measures at all, the outbreak could have caused more than half a million deaths in Britain and 2.2 million in the United States.
Even with the government's previous plan to control the outbreak - which involved home isolation of suspect cases but did not include restrictions on wider society - could have resulted in 250,000 people dying "and health systems...being overwhelmed many times over," the study said.
With the measures outlined - including extreme social distancing and advice to avoid clubs, pubs and theatres - the epidemic's curve and peak could be flattened, the scientists said.
"This is going to place huge pressure on us as a society, and economically," said Azra Ghani, a professor of infectious disease epidemiology at Imperial who co-led the work with Ferguson.
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This study helped change the British government's position, according to those involved with the decision. The government said it had accelerated its plans "the advice of the experts" and that the new measures had always been "part of the government's action plan".
"We continue to follow the science and act on the advice of the experts, which is that we are bringing in these more substantial measures slightly faster than we originally planned," the source said.
Tim Colbourn, an expert in global health epidemiology at University College London said the projections in the study signalled "tough times ahead".
"The results are sobering," he said.
Below are some of the findings of the research:
* If no action had been taken against the virus it would have caused 510,000 deaths in Britain and 2.2 million in the United States, the study said.
"The epidemic is predicted to be broader in the U.S. than in GB and to peak slightly later. This is due to the larger geographic scale of the US, resulting in more distinct localised epidemics across states," the study said.
* The British government's previous plan to control the virus involving home isolation of suspect cases, but not including restrictions on wider society, could have resulted in 250,000 people dying, the researchers said.
The approach would "likely result in hundreds of thousands of deaths and health systems (most notably intensive care units) being overwhelmed many times over," the study said.
* The study said that a strategy of draconian restrictions was the best way to tackle the virus.
"We therefore conclude that epidemic suppression is the only viable strategy at the current time. The social and economic effects of the measures which are needed to achieve this policy goal will be profound," the study said.
"Many countries have adopted such measures already, but even those countries at an earlier stage of their epidemic (such as the UK) will need to do so imminently."
* The study said that 9% of people in the most vulnerable age group, 80 and older, could die if infected.
* The health impacts from coronavirus are comparable to the devastating 1918 influenza outbreak.
"The last time the world responded to a global emerging disease epidemic of the scale of the current COVID-19 pandemic with no access to vaccines was the 1918-19 H1N1 influenza pandemic," the study said.
* To curb the epidemic, the restrictions being in place until a vaccine was found in 12 to 18 months, the research said.
"The major challenge of suppression is that this type of intensive intervention package – or something equivalently effective at reducing transmission – will need to be maintained until a vaccine becomes available (potentially 18 months or more) – given that we predict that transmission will quickly rebound if interventions are relaxed," the study said.