Recent reports indicate that the pandemic H1N1 virus is causing much more strain on the health care system in the United Kingdom this flu season than last year. For example, approximately 50% of all critical care beds are currently occupied by people infected with pandemic H1N1. And this is occurring early in the flu season. The peak in infections is likely weeks away.
Why this unprecedented pressure on the health care system in the UK? The relatively low rate of vaccination in the UK has been put forward as one explanation. However, no vaccine was available for the peak of infections in the previous flu season, so this cannot be the reason for the unprecedented number of very ill people this flu season. Advertising directed at improving hygeine was cut from the budget this year, but has recently been reinstated. If this is the reason for the difference, we should expect a dramatic reduction in cases in the near future. Last year, Tamiflu was easily obtained in the UK. However, there have been no media reports indicating that the policy on prescribing Tamiflu has changed this year.
The most disturbing possible explanation for the difference between last year and this year is that a new strain of pandemic H1N1 is now circulating in the United Kingdom. One argument in favor of this hypothesis is the disproportionate number of severe cases and deaths originating in North West England. Six people have died in Merseyside alone.
Flu viruses can become more dangerous in two ways: they can spread more easily and they can become more lethal. At this point, it is not possible to determine whether the pandemic H1N1 virus has changed in one or both of these ways in the United Kingdom. However, it is worth pointing out that a recent publication suggests that pandemic H1N1 has the potential to become more pathogenic.
From Ilyushina et al. 2010:
Our data showed that the acquisition of two nonsynonymous mutations in the HA (K154Q) and PA (L295P) genes resulted in rapid selection of the pandemic virus with improved replication and virulence.
We believe that surveillance should involve careful examination of the adaptive changes identified here as possible markers for enhanced morbidity of the pandemic viruses. In conclusion, our study demonstrates that the emergence of a more virulent A/H1N1 pandemic strain is possible.
To detect the subtle changes described in the paper above, it is essential that all 8 genomic segments be sequenced from fatal cases. Further, this data should be made immediately available to all scientists by depositing the sequences in one of the publicly available databases: EMBL, DDBJ or GenBank.
Ilyushina et al. (2010) Does Pandemic A/H1N1 Virus Have the Potential To Become More Pathogenic? mBio, Nov 16;1(5). pii: e00249-10.