Sarah Boseley Health editor
Feb. 27, 2020
Reports that a woman in Japan has tested positive for the Covid-19 disease for a second time, after seemingly recovering, will alarm scientists and public health experts trying to control the spreading epidemic, and underlines how much we still do not know.
There are a number of possible explanations for the second positive test of the woman, in her late 40s, a resident of Osaka who worked as a tourbus guide. She first tested positive for coronavirus in late January and was discharged from hospital on 1 February after recovering, before testing negative on 6 February.
It is possible, say experts, that when the woman was released, she had not cleared the virus. But if so, that means it lingered dormant in her body longer than the 14-day quarantine period. She will have been in contact with more people than have been traced, which poses worrying questions about the length of time people should be isolated after a positive test.
Alternatively, she may have been wrongly diagnosed with Covid-19 the first time round. But nobody is ruling out the possibility of reinfection. Once the immune system has fought off viral or bacterial infections, it generally recognises them and can block them the next time they are encountered – but not always and the protection may not last.
There have been reports of a few cases of reinfection in China, but doctors will hope it occurs in just a very few individuals, if at all.
After more than 82,000 cases of Covid-19, the unknowns still outnumber the knowns. Although there is clearly human-to-human transmission, we don’t know whether that happens only through droplets from coughs or sneezes or whether there is some aerosol transmission as well, which would mean the virus can travel greater distances through the air. There have been reports of airborne transmission in China, although the World Health Organization (WHO) says it is generally not happening.
However, the infection of large numbers of people on board the Diamond Princess cruise liner, which did not end after people were told to remain in their cabins, still needs explanation. Droplets from someone who is infected can spread to others within 1 to 2 metres. But the Sars (severe acute respiratory syndrome) virus, which is very similar, spread through the air via the plumbing in the Amoy Gardens apartment block in Hong Kong in March 2003, where it infected more than 300 people, and then reached other blocks nearby, over a distance of up to 200 metres.
And while we know there is asymptomatic transmission from somebody with the new coronavirus who is not ill, we do not know how extensive that is. Some people, known as “super-spreaders”, are more efficient transmitters of viruses than others.
What is Covid-19 - the illness that started in Wuhan?
It is caused by a member of the coronavirus family that has never been encountered before. Like other coronaviruses, it has come from animals. Many of those initially infected either worked or frequently shopped in the Huanan seafood wholesale market in the centre of the Chinese city.
Have there been other coronaviruses?
Severe acute respiratory syndrome (Sars) and Middle Eastern respiratory syndrome (Mers) are both caused by coronaviruses that came from animals. In 2002, Sars spread virtually unchecked to 37 countries, causing global panic, infecting more than 8,000 people and killing more than 750. Mers appears to be less easily passed from human to human, but has greater lethality, killing 35% of about 2,500 people who have been infected.
What are the symptoms caused by the new coronavirus?
The virus can cause pneumonia. Those who have fallen ill are reported to suffer coughs, fever and breathing difficulties. In severe cases there can be organ failure. As this is viral pneumonia, antibiotics are of no use. The antiviral drugs we have against flu will not work. Recovery depends on the strength of the immune system. Many of those who have died were already in poor health.
Should I go to the doctor if I have a cough?
UK Chief Medical Officers are advising 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 who is experiencing a cough or fever or shortness of breath to stay indoors and call NHS 111, even if symptoms are mild.
Is the virus being transmitted from one person to another?
China’s national health commission has confirmed human-to-human transmission, and there have been such transmissions elsewhere.
How many people have been affected?
As of 20 February, China has recorded 2,118 deaths from the Covid-19 outbreak. Health officials have confirmed 74,576 cases in mainland China in total. More than 12,000 have recovered.
The coronavirus has spread to at least 28 other countries. Japan has 607 cases, including 542 from a cruise ship docked in Yokohama, and has recorded one death. There have also been deaths in Hong Kong, Taiwan, France and the Philippines.
There have been nine recorded cases and no fatalities to date in the UK. As of 17 February, a total of 4,501 people have been tested in the UK, of which 4,492 were confirmed negative.
Why is this worse than normal influenza, and how worried are the experts?
We don’t yet know how dangerous the new coronavirus is, and we won’t know until more data comes in. The mortality rate is around 2% at the centre of the outbreak, Hubei province, and less than that elsewhere. For comparison, seasonal flu typically has a mortality rate below 1% and is thought to cause about 400,000 deaths each year globally. Sars had a death rate of more than 10%.
Another key unknown is how contagious the coronavirus is. A crucial difference is that unlike flu, there is no vaccine for the new coronavirus, which means it is more difficult for vulnerable members of the population – elderly people or those with existing respiratory or immune problems – to protect themselves. Hand-washing and avoiding other people if you feel unwell are important. One sensible step is to get the flu vaccine, which will reduce the burden on health services if the outbreak turns into a wider epidemic.
Is the outbreak a pandemic?
A pandemic, in WHO terms, is “the worldwide spread of a disease”. Coronavirus cases have been confirmed outside China, but by no means in all 195 countries on the WHO’s list. It is also not spreading within those countries at the moment, except in a very few cases. By far the majority of cases are travellers who picked up the virus in China.
Should we panic?
No. The spread of the virus outside China is worrying but not an unexpected development. The WHO has declared the outbreak to be a public health emergency of international concern. The key issues are how transmissible this new coronavirus is between people, and what proportion become severely ill and end up in hospital. Often viruses that spread easily tend to have a milder impact. Generally, the coronavirus appears to be hitting older people hardest, with few cases in children.
The WHO says we still need more information about the severity of the disease. In China, where the vast majority of cases and deaths have so far occurred, we know that 81% of people have had only mild illness. Of the rest, 14% have severe disease, which may become pneumonia, and 5% have critical disease involving breathing problems and organ failure. The death rate has been estimated at between 2 and 4% in Wuhan, where the epidemic began, but only 0.7% in the rest of China. But we still do not know how many people are not being counted in these statistics, because they suffer only a sore throat and do not go to hospital.
It is clear that those people with damaged or failing immune systems are most at risk. “Older people, and those with pre-existing medical conditions (such as high blood pressure, heart problems or diabetes) appear to be more vulnerable,” says the WHO. But we do not know why children, who are very susceptible to some diseases, do not seem to be much affected by Covid-19.
We do not know whether any of the antiviral drugs in existence will help people recover – some, including anti-HIV/Aids drugs, are being given to patients as part of trials in China. We are probably at least 18 months away from knowing whether there can be an effective vaccine against Covid-19.
And we don’t know where and how this all began. Scientists understand from the DNA of the virus that it came from animals, as did the other problematic coronaviruses, Sars and Mers (Middle East respiratory syndrome). Because of a cluster of early cases linked to the Huanan seafood market in Wuhan, which sold and slaughtered live animals for food, most believe the likely source to be wild animals. The similarity of the virus to Sars suggests a bat origin, but there would have been an intermediary animal carrying the virus, which could have been civet cats, bamboo rats or – as one Chinese university has claimed – pangolins.
The earliest recorded case of Covid-19 was in someone who had no link to the market, raising questions about this theory, but it is not possible to be sure that patient was the first, not least because of the large proportion of people with mild illness.
