Still in the Dark

The spread of the novel influenza A(H1N1) virus through North America is nearly complete. Only three continental US jurisdictions (Wyoming, West Virginia and Alaska) and three Canadian provinces or territories (Newfoundland, Nunavut and the Northwest Territories) haven't reported cases. Its progress elsewhere is still slow, however. Japan (163 cases), Spain (103), the UK (102) and Panama (54) lead; vigorous containment is still the order of the day in the UK. But unless the North American epidemic slows soon, the continued export of the virus – in the coughs and sneezes of infected travellers returning home (particularly to the southern hemisphere, which is just entering its flu season) – has a good chance of defeating all best-laid plans. And it is doing well in Japan.

The US Novel Swine-Origin Influenza A(H1N1) Investigation Team have analysed the first 642 confirmed cases in the US. A new for flu observation was vomiting and diarrhoea in 25 per cent of confirmed cases. Perhaps 'gastric flu', a condition hitherto denied by medical science, really exists. On the whole, however, the description is fundamentally of seasonal flu behaving unseasonally – and seasonal flu can be very nasty for some. According to the most recent CDC 2008-9 Influenza Season Update, 59 influenza-associated paediatric deaths have occurred in the US since 28 September 2008.

The WHO Rapid Pandemic Assessment Collaboration (mathematical modellers and epidemiologists from the UK, Mexico and Switzerland) used early data to analyse the Mexican outbreak. They estimate that 23,000 people had been infected by late April, with a clinical severity less than in the pandemic of 1918 but similar to that in 1957, and with transmissibility higher than seasonal flu. Their determination of a case fatality rate of 0.4 per cent looks pessimistic, going by the US numbers (5123 confirmed or probable cases so far with six deaths). Perhaps this has something to do with their models being rich in assumptions and their study being quick and dirty – as it had to be at this early stage.

The comparison with 1957 is helpful. It remains the biggest pandemic since 1918 and so is an essential benchmark for planners. I remember the exact spot on the Albert Embankment where the new H2N2 virus first seized me by the throat. Like novel A(H1N1) it started by infecting schoolchildren. A significant number of them died during the first month of the epidemic in Britain. But it wasn't like 1918. The majority of the deaths in 1957 were caused by staphylococcal pneumonia (the bacterium infects lungs damaged by the virus). In 1918 this was rare, with lots of deaths being caused by the virus alone.

There is another lesson from the past. At the peak of the 1957 pandemic in the US, fewer died from influenza/pneumonia than in the flu season of 1953. Canada and England had bad flu epidemics in 1951 ( in Liverpool the weekly death toll surpassed that of 1918); twice as many died as in 1957. So while pandemics are bad for populations because the new virus infects many more than in an average flu year, and disruptive for society because so many fall ill at the same time, they may well be no worse for the individual than seasonal flu in a bad year.

At a World Health Organisation assembly that began in Geneva yesterday, Britain and Japan made bids to redefine the term 'pandemic' – in essence to say that even if the virus takes off outside the Americas (the epidemiological definition) it shouldn't count as one unless it's as nasty as the pandemic planners predicted. Welcome to the looking glass world of public health politics: '“When I use a word," Humpty Dumpty said in a rather scornful tone, "it means just what I choose it to mean."’