The current global influenza situation is characterized by a number of trends that must be closely monitored, says the World Health Organization (WHO) in a recent briefing document.
According to WHO these trends include:
- An increase in the variety of animal influenza viruses co-circulating and exchanging genetic material, giving rise to novel strains;
- Continuing cases of human H7N9 infections in China; and
- A recent spurt of human H5N1 cases in Egypt.
- Changes in the H3N2 seasonal influenza viruses, which have affected the protection conferred by the current vaccine, are also of particular concern.
The highly pathogenic H5N1 avian influenza virus, which has been causing poultry outbreaks in Asia almost continuously since 2003 and is now endemic in several countries, remains the animal influenza virus of greatest concern for human health. However, over the past two years, H5N1 has been joined by newly detected H5N2, H5N3, H5N6, and H5N8 strains, all of which are currently circulating in different parts of the world. In China, H5N1, H5N2, H5N6, and H5N8 are currently co-circulating in birds together with H7N9 and H9N2.
“The diversity and geographical distribution of influenza viruses currently circulating in wild and domestic birds are unprecedented since the advent of modern tools for virus detection and characterization. The world needs to be concerned,” states WHO.
Virologists interpret the recent proliferation of emerging viruses as a sign that co-circulating influenza viruses are rapidly exchanging genetic material to form novel strains.
The emergence of so many novel viruses has created a diverse virus gene pool made especially volatile by the propensity of H5 and H9N2 viruses to exchange genes with other viruses. The consequences for animal and human health are “unpredictable yet potentially ominous” says WHO.
On many levels, the world is better prepared for an influenza pandemic than ever before, according to WHO. However, the level of alert is high and although the world is better prepared for the next pandemic than ever before, it remains highly vulnerable, especially to a pandemic that causes severe disease. Nothing about influenza is predictable, including where the next pandemic might emerge and which virus might be responsible. The world was fortunate that the 2009 pandemic was relatively mild, but such good fortune is no precedent, says WHO.