Scientists are racing to understand the coronavirus disease, Covid-19, which emerged in China in December. The number of confirmed cases worldwide is more than 10 times higher than the 8,100 known to have been infected by Sars, a related virus that caused a six-month epidemic in 2003.
Though Covid-19 has passed its peak in China, it is spreading rapidly elsewhere with the number of cases in some countries doubling every week. Public health experts fear the respiratory illness, which is believed to have started in a food market in Wuhan, may become the most serious pandemic since Spanish flu in 1918-19. The World Health Organisation is trying to contain the infection before it reaches that stage.
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How dangerous is the new coronavirus?
Covid-19 is transmitted more readily between humans than Sars, though it is less virulent. Computer modelling suggests that each new case infected 2.5 other people on average in the early stages of the epidemic, though Chinese authorities have greatly reduced this "reproduction number" through drastic action to isolate cases and trace their contacts.
The virus has caused severe respiratory disease in about 20 per cent of patients and killed more than 3 per cent of confirmed cases. Sars killed 10 per cent of infected individuals. Older people, whose immune defences have declined with age, and those with underlying health conditions are much more vulnerable than the young.
But fatality rates are hard to estimate in the early stages of an outbreak and depend on the medical care given to patients. For example, ventilators save lives by enabling people with pneumonia to breathe. Most experts believe the current fatality rate is exaggerated by serious under-diagnosis of mild cases and Covid-3 is likely to have a fatality rate of 1 to 2 per cent in a population with good healthcare.
For comparison, seasonal flu has a mortality rate below 0.1 per cent but it infects so many people that it results in about 400,000 deaths a year worldwide. Spanish flu infected an estimated 500m people and killed 50m worldwide in 1918-19.
How does the virus spread and what is the incubation period?
To catch Covid-19, you need to be physically close to someone shedding significant amounts of virus — which almost always means a person with symptoms of disease, though asymptomatic transmission may occur, albeit very rarely.
Respiratory infections are most commonly spread through the air by viral particles in droplets from a cough or sneeze, though health workers and family members are also vulnerable to infection through close physical contact with patients without good barrier protection.
The incubation period between infection and symptoms appearing can range from two to 14 days. About five days is most common, according to the WHO.
Can you catch coronavirus during air travel?
Yes, if you are close to someone shedding virus in the aircraft cabin, just as you could in any enclosed space. That probably means sitting within two rows of them. People worry about germs being spread by the cabin air circulation system, but modern planes are very efficient at removing viral particles.
Since proximity is the main risk factor for infection, you may be in more danger while queueing at the departure gate — or travelling to or from the airport by taxi or public transport. There is also a risk of infection from the virus surviving on surfaces such as aircraft toilet doors or tray tables, so it is worth washing your hands frequently while travelling and/or applying an alcohol-based hand rub.
Do masks help protect against infection?
Although wearing face masks appears socially obligatory in some east Asian cities affected by coronavirus, the WHO says healthy people do not need to wear a mask unless they are taking care of a person with suspected Covid-19 infection. But it does advise people in places where there are Covid-19 cases to wear a mask in public if they are coughing or sneezing.
The most effective ways to protect yourself and others against Covid-19 are to clean your hands frequently, keep them away from your face, cover coughs and sneezes with the bend of your elbow or a tissue, and keep at least a metre away from people who are coughing or sneezing.
What happens when you are infected?
The virus multiplies within the lower respiratory tract, where symptoms develop. Early ones are a fever and cough. Most people will recover within a few days. But about 20 per cent go on to develop serious pneumonia as their lungs become inflamed; they may need a respirator to help them breathe.
In some of the most severe cases, there can even be a "cytokine storm" in which the immune system goes into overdrive, overwhelming the body with cells and proteins that destroy other organs.
How can doctors tell whether a patient has coronavirus disease?
Since Chinese scientists published the genetic sequence of the virus on January 10, laboratories anywhere in the world have been able to test patient samples for its presence. They use a procedure called polymerase chain reaction (PCR) to amplify and identify viral genes. But PCR is slow and requires specialist equipment, so researchers are rushing to develop faster, cheaper and more portable tests.
At the same time scientists are carrying out detailed analysis of the full genetic code of virus isolated from Covid-19 patients to trace mutations that might make it more or less virulent or transmissible as the epidemic proceeds. It seems more genetically stable than flu, with no significant changes detected.
A third level of testing getting under way ìnvolves looking for antibodies in populations exposed to Covid-19, which will show how many people were infected but developed mild or no symptoms. This "serological" testing takes longer but should soon give results in China.
Can you be infected more than once?
Reports continue to emerge of coronavirus "reinfecting" people who had apparently cleared the disease, but experts are casting doubt on whether reinfection is taking place. A more likely scenario than reinfection is that the immune system suppressed coronavirus to a low level — too low to detect in viral tests of swabs from the patients — and the virus then surged back, causing symptoms to reappear.
How frequently this occurs — and whether it poses a serious risk to efforts to control the spread of Covid-19 infection — is unknown. Medical specialists still have much to learn about the natural history of the new coronavirus and its interaction with the human immune system. If reinfection really does take place because people mount a very weak response to infection, that would be bad news for the development of a vaccine.
Are drugs and vaccines being developed?
No existing drugs are designed to treat coronaviruses, though some antiviral medicines may alleviate the symptoms. Chinese doctors are prescribing drugs normally prescribed for HIV — and another antiviral called remdesivir that was developed to treat Ebola. They expect to report within weeks whether the drugs help against Covid-19.
Programmes to develop vaccines quickly to prevent Covid-19 infection are under way in dozens of academic and private labs around the world, some under the auspices of the Oslo-based Coalition for Epidemic Preparedness Innovations (Cepi) — a US$750m partnership set up in 2017 by governments, industry and charities to prevent future pandemics.
Last month, Moderna, a US biotechnology company, delivered the first vials of its candidate vaccine to the National Institutes of Health for testing in healthy human volunteers. NIH expects a clinical trial with about 20 to 25 volunteers to start in April, with initial results available this summer. But even if all goes well, no vaccine is likely to be available for widespread use until early next year.
Why hasn't the WHO declared coronavirus a pandemic?
The WHO remains reluctant to talk about a pandemic — sustained transmission of disease in different parts of the world — although many epidemiologists say one is already under way.
Tedros Adhanom Ghebreyesus, WHO director-general, spelt out the rationale. "Using the word pandemic carelessly has no tangible benefit, but it does have significant risk in terms of amplifying unnecessary and unjustified fear and stigma, and paralysing systems. It may also signal that we can no longer contain the virus, which is not true," he said. In other words, it might create panic and overreaction.
WHO took the key step of declaring a Public Health Emergency of International Concern on January 30. Officially calling Covid-19 a pandemic would be symbolically important but would make little practical difference. The last recognised "pandemic" was H1N1 flu in 2009.
How is the epidemic likely to develop?
Although scientists have learnt an astonishing amount about Covid-19 in the months since the disease was first detected in Wuhan, they do not know yet enough about it to forecast likely outcomes with any accuracy.
There are various possible scenarios. One extreme is that the disease might spread worldwide and affect as much as half the global population within a year, overwhelming health services and killing tens or even hundreds of millions of people. But the WHO is still promoting an optimistic scenario in which determined action contains Covid-19 to specific regions and suppresses it.
Written by: Clive Cookson
© Financial Times