Swine flu may be more infectious than so far appears in the UK and the current guidance on catching it may have to be changed, the chief medical officer, Sir Liam Donaldson, warned today.
The World Health Organisation concurred, saying that if unchecked, swine flu could affect almost a third of the population – 2 billion people.
Although currently it is only mild, the attack rate of the strain now affecting 23 countries is around 25-30%, Donaldson said, although he added that it was possible people over the age of 50 might have some immunity to the virus.
In the UK, the Health Protection Agency says that only those who have been within one metre of an infected person for more than an hour are considered to be at risk. "I think it will be more transmissible than that when it gets going," said Donaldson. "We may need to look at that advice."
Anybody with flu-like symptoms is already being told to stay at home to avoid infecting other people. He said that if flu spreads and becomes more severe, particularly in the winter months, there will be concerns about people working at close quarters in offices and travelling together on tubes, trains and buses.
Donaldson, giving a joint briefing in London with Alan Johnson, the health secretary, said the top laboratories in the world were still analysing the flu strain now said to have killed 42 people in Mexico, which also has 1,112 confirmed cases. "We have to wait another few weeks for characterisation of the virus," he said.
Last night five swine flu cases were confirmed in Brazil and Argentina. Brazilian Health Minister Jose Gomes Temporao said four young adults contracted the flu outside the country - three in Mexico, and one in Florida. Prior to Thursday, Colombia was the only South American nation to confirm swine flu with its borders.
In Mexico and in the USA – which Donaldson said was about a month behind Mexico in the progress of its flu outbreak – the picture looks different to here, with many more cases apparently transmitted from one human to another. Only 10 of the 34 cases confirmed in the UK were actually acquired here.
On the possibility that people over the age of 50 might have some immunity to the virus, which is of the H1N1 strain, Donaldson said: "H1N1 has been around a long time. It was a sub-type of the Spanish flu and is in our current seasonal flu vaccine. The optimistic interpretation is that the immune systems of the over-50s might have some memory of the H1N1 of this kind."
He and Johnson defended their handling of the flu outbreak against critics who say it should be treated just like a mild seasonal flu, without school closures or the handout of antiviral drugs to contacts of those who are sick.
"We don't know enough about the illness at this stage. It is very reassuring that cases so far are not worse. We don't want a situation where a child is admitted to hospital because of the complications of flu. As far as children are concerned, I'm very, very cautious. Simply to allow people to be exposed to it and develop antibodies I don't think is the right approach."
Johnson said he would rather have egg on his face than deaths on his hands. "I'd rather be accused of over-hyping something and exaggerating than not be prepared for a general pandemic that seriously affected our citizens," he said. The current strategy of containment justified using "precious antiviral drugs", he said. If it became widespread or more severe, the strategy would change to reduce the numbers of people given drugs on a preventive basis. Patients and their family members would receive drugs, but not others who might have been in contact.
School closures, on the advice of the Health Protection Agency, were a necessary part of the containment strategy. Johnson said the public response to the flu threat had been good, but "now the danger is complacency".
The government has ordered 227 million face masks and 34 respirators for health workers and has spent between £400m and £500m on its stockpile of flu drugs, which is being expanded to cover 80% of the population from 50% now; £100 million has been committed in contracts to drug companies Baxter and GlaxoSmithKline to produce a vaccine once the strain is understood.
