Swine flu can infect cells deeper in the lungs than seasonal flu, making people who catch it more likely to develop serious complications, research suggests. The study published in the journal Nature Biotechnology provides the first laboratory corroboration of reports from front-line doctors.
Seasonal strains of flu attach themselves almost exclusively to cells found in the nose, throat and upper airway, producing some of influenza’s signature symptoms: a runny nose, scratchy throat and a dry cough. But the research shows that swine flu — by sticking to a greater range of receptors — can also breach cells deep in the lungs.
It comes as the U.K. Government’s chief scientific adviser said that swine flu could reach a peak in the next month or so. Professor John Beddington said that a second wave of infections was expected “not much before October at the earliest”. Thereafter research and epidemic modelling suggested the virus would be weakened, he said. “You can get infections coming back in a number of waves but it’s likely that the next one will be larger than any subsequent ones,” Professor Beddington told the British Science Festival at the University of Surrey.
The Government revised its planning assumptions for the swine flu pandemic last week, with 19,000 people in Britain expected to die in the “worst-case scenario”. A previous estimate put the figure at 65,000. However, it is still estimated that up to 30% of the population will fall ill. While most will get better within a week or so, some may develop secondary infections or pneumonia, which can be fatal.
At least 70 people in Britain have died after contracting swine flu and hundreds have required hospital treatment.
In the latest research, Professor Ten Feizi and colleagues at Imperial College London carried out laboratory experiments in which 86 different receptors were exposed to seasonal and pandemic flu.
Influenza viruses penetrate cells by attaching themselves to molecules called receptors, located on the outside of the cell wall.
The seasonal strains only locked onto the kind of receptors found in the upper respiratory track. But the swine flu virus was also able to latch onto receptors found inside the lungs, although more weakly. The adhesion results in a more severe lung infection.
Professor Feizi said: “If the flu virus mutates in the future, it may attach to the receptors deep inside the lungs more strongly, and this could mean that more people would experience severe symptoms. “We think scientists should be on the lookout for these kinds of changes in the virus so we can try to find ways to minimise the impact.”
Some experts and critics of the Government have suggested that there will not be enough NHS intensive care beds in the NHS to cope with the demand expected in a second wave of the pandemic. But how severe the outbreak is will depend largely on how many people have already had the illness, Professor Beddington added. “It’s difficult to estimate the number of unreported cases,” he said..
“Someone could just feel a bit sniffly and irritable but actually have the virus. If this applies to a large fraction of the population then the second wave will be small.”
So far about 450,000 doses of the drug Tamiflu (oseltamivir) have been distributed, 10 times the number of confirmed flu cases.
Professor Beddington defended the decision to treat large numbers of the population with antiviral drugs, but admitted that the official Scientific Advisory Group for Emergencies (Sage) had been divided on whether Tamiflu should be made universally available.
Some members of the group, which advises the Cabinet, had feared that providing antivirals to everyone infected risked the virus developing resistance, he said. But he added that there was little evidence that the virus had built up any resistance.