Flu pandemic: what lies ahead

Thursday 11 February 2010 Pandemic is heading for ‘post-peak’ period, WHO says amid lingering concerns over unpredictable future
Source: CDC/Jim Gathany	The 2009 pandemic is waning in most parts of the world, but recently Senegal has reported the first 14 cases of ‘swine flu’ to be associated with community transmission of the virus in West Africa, the World Health Organization (WHO) said today. “There is a scientific judgment that the worst on a global level may be over,” said Keiji Fukuda, Special Adviser on Pandemic Influenza to the Director-General, at a news conference. “‘However it’s also very clear that the virus has not disappeared. We can anticipate significant local upsurges.” This pattern of activity for the new virus is different from patterns documented a few months ago, explained Fukuda, and could mean that the pandemic has entered a period of transition into “regular” flu activity dubbed the ‘post-peak’ period in the WHO pandemic guidance document. But a formal assessment of this will be made later this month in the 7th meeting of an advisory body, the International Health Regulations (IHR) Emergency Committee. In a different meeting to be held on 18 February, the WHO will decide which virus strains to recommend for companies making the vaccine that will be distributed in the northern hemisphere in the next flu season. Seasonal flu viruses have not disappeared, said Fukuda, but the swine-origin H1N1 strain is now dominating. “I don’t want to second guess what the expert advisers will recommend; but it is fair to point out that the current pandemic virus is by far the most common being isolated.” Juergen Richt, from Kansas State University in the USA, is worried about the far-reaching spread of this highly transmissible virus. As it becomse the dominant strain, it is more likely to circulate in the same areas that harbour the H5N1 bird-flu strain. If this happens, “it could be big trouble”, he says. Although the swine-flu virus has not been found to infect chickens, where the H5N1 strain is commonly found, both viruses could infect humans at the same time — a window of opportunity to re-assort. Because the new H1N1 virus spreads more easily than the seasonal H1N1 and H3N2 strains, Richt believes that the chances of the two virus subtypes swapping genetic material in this way are higher than they were before the pandemic strain emerged. A transformation of the H5N1 virus “could be only a couple of mutations away”, says Richt. Swapping genes with the new H1N1 virus might allow it to transmit more efficiently, creating a very different pandemic scenario. Fukuda said today that all the pandemic-H1N1 strains analysed so far look very similar, so this virus subtype appears to be very stable. But in a world of fickle flu viruses the H5N1 strain appears especially unstable. According to results from an influenza-A genome-mapping project published this month in PLoS ONE, H5N1 viruses appear to swap genetic material with other virus subtypes often, but fail to accumulate enough mutations to allow efficient spread between people. The authors say that this suggests a low pandemic risk for this strain “in its current form”. Raul Rabadan from Columbia University in New York, USA, cautions that “although we are learning more about these viruses, we still do not have a complete understanding of all factors that could contribute to the efficient propagation of influenza viruses in humans.” “Viruses are so flexible”, says Richt. One never knows what might be around the corner, he points out, so keeping surveillance efforts going is essential.