A new strain of bird flu which kills 38 per cent of those it infects has been identified by the deputy chief medical officer for England as the most likely candidate to spark a worldwide flu pandemic.
Professor Jonathan Van-Tam, deputy chief medical officer for England with special responsibility for emergency preparedness and pandemic planning, told the Telegraph that the virus concerning him and others most was H7N9, a flu virus circulating in poultry in China.
Scientists across the world are on high alert for what the World Health Organisation (WHO) has dubbed “disease X” - a newly emerging pathogen that could prove as destructive as the 1918 Spanish flu which killed between 50 and 100m people a century ago.
Prof Van-Tam said the UK government was gathering as much intelligence on the H7N9 virus as possible – looking at its geographic spread, the number of human cases and any changes in its genetic structure.
“[H7N9] is an example of another virus which has proven its ability to transmit from birds to humans. It’s possible that it could be the cause of the next pandemic,” he said.
So far 1,625 people in China are known to have been infected with the H7N9 virus, 623 of whom have died. Most of those infected have been been in close contact with poultry or poultry markets.
It is unknown how long the virus has been circulating among birds but it was first identified in humans in 2013. In birds, the virus generally does not cause any symptoms, but in humans it can cause serious illness and – in almost 40 per cent of cases – death.
H7N9 can not yet be passed from one person to another but experiments on animals have shown that it was just three mutations away from being able to do so.
H7N9 is younger and stronger [than H5N1] and is now waiting for its opportunity
John Oxford, professor of virology
People who contract H7N9 develop a high fever, cough and shortness of breath and it can rapidly progress into severe pneumonia. Those with the severe form of the disease develop acute respiratory distress syndrome – where the lungs cannot provide the body with enough oxygen – septic shock and multi-organ failure.
Pregnant women, older people and those with underlying conditions are most likely to become seriously ill or die, according to the World Health Organization.
H7N9 belongs to a family of type A flu viruses and is closely related to avian bird flu – H5N1, which crossed into humans in 2003. Bird flu has killed around 400 people globally but has not yet sparked a worldwide pandemic.
John Oxford, professor of virology at Queen Mary University of London, said that bird flu was always through to have pandemic potential and the new strain was a concern.
“H5N1 was first isolated in 1997 and has had 19 years to float around. It’s had its chance to cause a worldwide pandemic but it looks like it’s not going to do it. But H7N9 is younger and stronger and is now waiting for its opportunity,” he said.
The 1918 Spanish flu had the highest death rate of all known flu pandemics, killing between 2 and 2.5 per cent of all those who contracted it globally. However death rates varied massively - from less than 1 per cent to over 40 per cent - depending on susceptibility and preparedness of the communities it affected.
More than a third of those who have so far contracted H7N9 die from the disease but that death rate would be unlikely to be replicated in a pandemic as the virus would change, said Prof Van-Tam.
“Mortality is about 38 per cent of known cases, higher than any of the human pandemic viruses. But it would be wrong to think we could have a pandemic virus in future that could kill 38 per cent of people. It would change,” he said.
The US Centers for Disease Control and Prevention (CDC) also ranks H7N9 number one on its influenza risk assessment tool as having the potential to cause a pandemic. The risk of it mutating into a pandemic virus is judged “moderate to high”.
Influenza viruses constantly change... it is possible that this virus could gain the ability to spread easily and sustainably among people
US Centers for Disease Control and Prevention
“Influenza viruses constantly change and it is possible that this virus could gain the ability to spread easily and sustainably among people, triggering a global outbreak of disease,” says the CDC.
It has the “greatest risk to severely impact public health if it were to achieve sustained human-to-human transmission”.
The highest number of cases of H7N9 infection were in the winter of 2016-17 when there were 460 cases. This year there were just three cases.
Professor Oxford said the waxing and waning of the virus was to be expected.
“It might be to do with climate, it might be to do with movement of people or movement of geese, ducks or swans. It's normal,” he said.
Dr Jonathan Quick, a former director at the World Health Organization and author of the End of Epidemics, said that sustained human-to-human transition of H7N9 "would take a significant, successful mutation or a very, very unfavourable combination of social, environment factors, healthcare and political factors".
But he said that just before the 2014 Ebola outbreak, which killed 11,000 people in West Africa, the disease had been classed by experts as highly unlikely to lead to an epidemic.
"The West Africa outbreak was so much more explosive than the previous 22 outbreaks in Africa not because of any particular change in the virus, but because of the social, political and healthcare context in which it broke out. We had never before seen 'urban Ebola', which required a different approach," said Dr Quick.
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