New cases of the novel coronavirus or Covid-19 continue to be reported around the world.
There is widespread speculation that the illness could soon reach “pandemic” proportions – if it hasn’t already.
What does the term mean? And how worried should you be?
What is a pandemic?
There is no universally-agreed definition, but the word is usually applied to a new infectious illness – or a new strain of a previously-identified bug – spreading uncontrollably in different regions of the world.
Covid-19 might meet that definition because the virus was unknown to science before December last year, and because of the rate at which it is spreading across national borders.
Nearly 80,000 cases have been reported worldwide and more than 2,600 people have died, almost all of them in China.
Major new outbreaks have been reported in Italy, Iran and South Korea in recent days.
“Pandemic” comes from the Greek words for “all” and “people” but the word does not literally mean that an entire population becomes infected.
The most severe pandemic in recent history – the 1919 flu pandemic – infected around one third of the world’s population.
The word does not tell us anything about the severity of a disease: an illness could still be considered a pandemic if it caused no deaths.
When will a pandemic be declared?
The short answer could be: never. In previous large-scale outbreaks of illness, the World Health Organization has declared a pandemic. That’s what happened with the H1N1 strain of flu in 2009.
But the WHO no longer uses the same six-step system to describe the spread of disease.
Spokesman Tarik Jasarevic said: “There is no official category (for a pandemic). For the sake of clarification, WHO does not use the old system of six phases — that ranged from phase one (no reports of animal influenza causing human infections) to phase six (a pandemic) — that some people may be familiar with from H1N1 in 2009.”
The organisation still considers the Covid-19 outbreak a public health emergency of international concern.
Spokeswoman Margaret Harris said the WHO might start describing coronavirus as a pandemic in communications if it meets the old definition.
Does Covid-19 already meet the definition?
Ms Harris said the WHO does not yet have evidence that the virus is spreading freely from person to person throughout whole communities.
She said there was a link in most cases between new outbreaks and cases already reported in Asia.
“What we are seeing at the moment are outbreaks and clusters of cases in multiple countries. Some countries have since stopped transmission. They must remain alert for the possibility of reintroduction.
“If it became clear that it is all around the globe and we are seeing systematic community transmission, then we would say this meets the definition of a pandemic.”
There was some disagreement among epidemiologists on whether the outbreak is likely to reach pandemic proportions – or if it already has.
David Heymann, professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine: “It is still a series of outbreaks, and countries where they are occurring should make every effort to stop transmission and all countries should prepare for more widespread occurrence if it happens.
“Transmissibility in the community is not yet fully understood – terms such as pandemic are distracting.
“What is necessary is to understand the current situation in each country.”
Prof Mark Woolhouse, Professor of Infectious Disease Epidemiology, University of Edinburgh, said: “A pandemic means an infectious disease is spreading out of control in different regions of the world.
“We already have a COVID-19 epidemic in China and, more recently, large outbreaks in South Korea, Iran and Italy. If those outbreaks cannot be brought under control, then COVID-19 would fit the criteria of a pandemic.”
Dr Bharat Pankhania from the University of Exeter Medical School, said: “We now consider this to be a pandemic in all but name, and it’s only a matter of time before the World Health Organisation starts to use the term in its communications.”
What do we know about Covid-19 so far?
A study published by the Chinese Center for Disease Control and Prevention last week found that coronavirus was more contagious than the related SARS and MERS viruses.
More than 80 per cent of patients had mild symptoms. People aged over 80 and with chronic illnesses were at most risk of dying.
The crude death rate was just over 2 per cent, but experts cautioned this turn out to be wildly inaccurate as more information about the spread of Covid-19 comes to light.
If it turned out that many mild cases were not reported to the authorities, the final mortality rate would have to be revised down dramatically.
What’s the risk to the UK?
The UK’s four Chief Medical Officers still assess the risk to this country as “moderate”. So far there have been 13 confirmed cases in Britain and no deaths.
Prof Woolhouse said: “Many different countries around the world may be sources of COVID-19 infections.
“This makes it much harder for any one country to detect and contain imported cases and trying to do so will place ever greater demands on national health systems.
“This will make large and difficult to control outbreaks more likely in the UK and many other countries.”
Other experts speculated that the infection rate could drop as the weather warms up, a pattern seen in previous epidemics.
The latest UK government advice is for anyone who has travelled to the UK from mainland China, Thailand, Japan, Republic of Korea, Hong Kong, Taiwan, Singapore, Malaysia or Macau in the last 14 days and is experiencing cough or fever or shortness of breath, to stay indoors and call NHS 111, even if symptoms are mild.