If the spread of the new coronavirus isn’t halted, it could infect 60 per cent of the world’s population and kill 1 in 100 of those infected – around 50 million people.
This is what Gabriel Leung, chair of public health medicine at Hong Kong University, told The Guardian newspaper on 11 February. Is he right? The short answer is that no one knows, because there are many things we still don’t know about the virus.
First, can we stop it spreading globally? So far, there have been over 40,000 cases in China, and 24 other countries have reported around 300 cases. The virus is spreading much more readily than other coronaviruses that have jumped from animals into people.
Halting its spread requires identifying and isolating those who are infected. This could be especially difficult because some people might be infectious even when they have only mild symptoms. And while the average time from people being infected to showing symptoms is around three days, it might sometimes be as long as 24 days – more than the two-week quarantine period currently recommended.
China is taking drastic measures to contain the virus, but it isn’t clear if they are working. There has been a fall in the number of new cases reported per day, but this could be due to hospitals being overwhelmed. It also seems China is now not counting people who test positive for the virus but don’t show symptoms.
There is a good chance that wealthy countries could contain the trickle of cases currently being detected. The worry is that the virus is already spreading widely in countries that lack the resources to detect it.
The head of the World Health Organization has warned that we may only be seeing “the tip of the iceberg”. If so, the chances of preventing a global pandemic are low.
That brings us to the next question: how many people will be infected if the virus goes global? It has been estimated that 24 per cent of the world’s population was infected by the 2009 H1N1 swine flu pandemic, despite older people having pre-existing immunity because they had been exposed to similar viruses.
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As far as we know, no one has any pre-existing immunity to the 2019 coronavirus. Each infected person also appears to be infecting two to four others on average, compared with 1.5 for flu. So Leung’s estimate of 60 per cent getting infected appears plausible, but we can’t say for certain.
“You can’t really gauge what’s going on with this,” says David Heymann at the London School of Hygiene and Tropical Medicine, who led the global response to the SARS outbreak in 2003.
The severity of the virus is also key. Early estimates of the death rate from new diseases are typically much higher than the true figure, because only serious cases are detected. For instance, it is now thought the 2009 flu killed 1 in 5000 people, far fewer than first feared.
Initial reports of a 2 per cent death rate from the 2019 coronavirus were based on dividing the number of deaths by the number of confirmed cases. But this doesn’t take into account the delay between people falling ill and either recovering or dying, or the fact that doctors were testing only people who already had pneumonia – the most serious cases.
Based on estimates of the number of mild cases going uncounted, Neil Ferguson of Imperial College London calculates that 1 per cent of those infected are dying – the same percentage used to calculate the 50 million deaths estimate. This could still be an overestimate, not least as treatments in development could reduce the death rate further.
But Leung’s estimate actually misses another potential cause of deaths due to the coronavirus – people dying because normal healthcare services are disrupted by the outbreak.
“The worry is not just those infected by the coronavirus itself, but all the services that will no longer run,” says Devi Sridhar at the University of Edinburgh, UK. “You will see all kinds of knock-on effects.”
These will be most serious in poor countries whose health systems are already struggling. For instance, children began dying from measles when vaccination stopped during recent Ebola outbreaks in Africa. “UNICEF calls these the uncounted dead,” says Sridhar.
However, even rich countries could struggle. The UK’s pandemic plans are for something of a similar magnitude to 2009 H1N1 flu, for instance, which killed up to 500,000 people globally.
Paul Hunter at the University of East Anglia, UK, thinks the coronavirus will end up killing even fewer people than the 2009 flu. “I don’t expect we will have that degree of fatality with this coronavirus, but I might be wrong,” he says. “If it is much worse than H1N1, then it would be horrendously difficult to handle.”
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