After talking to Dan Jernigan, one of the top flu specialists at the US Centers for Disease Control here in Atlanta, I feel a bit clearer about current expert thinking about the H1N1 almost-pandemic.
The good news is that the illness is on average similar in its severity to normal seasonal flu or perhaps just a little more virulent. Certainly the virus is nowhere near as dangerous as the new flu strains that have caused the great pandemics of the past, notable in 1918.
What is unusual is the age pattern of infection, which continues mainly to infect children and young adults. In the US, 60 per cent of cases have been in 5- to 24-year-olds.
The new strain is scarcely hitting old people, the main victims of seasonal flu. To some extent this may reflect the pattern with which H1N1 is moving through the community, with schools particularly affected, so that the elderly have been less exposed to the virus.
But tests suggest that older people are still protected to some extent by previous exposure to similar viruses. This would particularly apply to those born before the 1957 pandemic of H2N2 flu which swept away many of the old H1N1 strains dating back to 1918.
When I told Jernigan that, so far as I knew, I had never had flu, he said I was almost certainly wrong. I must have been infected in the past but the symptoms were not serious enough to register in my mind as flu.
Routine analysis of blood samples shows that 7-10 per cent of the US population – 21m to 30m Americans – is infected with flu virus in an average year. But many suffer nothing worse than a feverish cold.
So much for the scorn that we hear frequently health experts and others pour on people who complain about flu when the symptoms are supposedly not serious enough. “You just have a bad cold,” they are told. But it turns out not to be true that flu is bound to hit you with a high fever and lay you low for a week.
It seems that the new virus is less likely than seasonal flu to cause very mild cold-like symptoms but that remains to confirmed.
Meanwhile experts such as Jernigan continue to emphasize the unpredictability of new flu strains, while repeating the likelihood that the northern hemisphere will experience a more extensive H1N1pandemic after the flu season begins in the autumn. By then, however, a vaccine against the new strain should be in production.