What are super-spreaders?
Not everybody is equal when it comes to the transmission of infectious diseases. In fact, it has been established for at least two decades that there is something called the 20/80 rule – that a small core group of about one in five people transmit infections to far more people than the majority do.
How does a person become a super-spreader?
There are a number of theories, but no definite answer. Some speculate that it is to do with the immune system of the super-spreader, which may not be good at suppressing the virus or alternatively may be so good that they do not feel symptoms themselves so carry on transmitting it to others. But it is likely to be caused by multiple factors, possibly including getting a higher dose of the virus in the first place or being infected with more than one pathogen. One thing seems certain – it is impossible to know who will be a super-spreader and who will not.
Are there super-spreaders of the new coronavirus?
It seems so. The third British case was a man in his 50s who contracted the coronavirus infection at a conference in Singapore. He then travelled to France where he stayed with his family in a ski chalet in the Alpine resort of Les Contamines-Montjoie. Five people who were in the chalet, including a boy of nine, have tested positive for coronavirus since the man came back to the UK on an easyJet flight and was diagnosed in Brighton. Another Briton who was on holiday in the chalet flew back to his home in Mallorca and was admitted to hospital in Palma. The chief medical officer said four more people had tested positive in England – all of whom were also on the skiing holiday in France.
Among delegates to the Singapore conference was a man who flew in from Wuhan, China, who may himself have been a super-spreader. A number of others who were there and returned to other countries, in addition to the British man at the centre of the ski chalet cluster, are said to have fallen ill.
Does this happen with other infectious diseases?
Yes. Super-spreaders have been documented as far back as the early 1900s, when one woman infected 51 people with typhoid, even though she had no symptoms herself. More recently, one student at a high school in Finland infected 22 others with measles in 1998, even though eight of them had been vaccinated. Two people are thought to have infected 50 others with Ebola in the Democratic Republic of the Congo in 1995. In the 2002-03 Sars epidemic, most people were not very infectious, but a few super-spreaders in Singapore appear to have transmitted the virus to as many as 10 people each.