Influenza A (H7N9) virus [Updated Continuously]

[21.02.14 Latest Update] Dozens new cases and fatalities reported from China. Now a total of 355 cases, including 112 deaths have been reported. The Case Mortality Rate (CMR) is at 31.5%.

[Chart by Fred de Vries]

The influenza virus is notoriously unstable and changes via antigenic drift (small changes) and antigenic shift (great changes) into new variants. Because of these changes, the Influenza A virus can now be subdivided into several genotypes or subtypes that are named by their variants of Hemagglutinin (H) and Neuraminidase (N). To date, 17 different HA antigens (H1 to H17) and nine different NA antigens (N1 to N9) for influenza A are known.

The unusually virulent Spanish Flu (1918-1919) was an Influenza A (H1N1) virus as was the Mexican Flu of 2009. Since 2004 the deadly Bird Flu is circulating around the world and this is an Influenza A (H5N1) virus. New and existing viruses (or virii) can sometimes start to infect people.

Will it become the next pandemic? Nobody knows but the medical world already holds its breath. At the moment there is no evidence yet that the virus is being transmitted easily between humans although some family members seem infected.

As most influenza is seasonal, it is not surprising that this epidemic seems to peter out but new infections are expected to be reported in the autumn of 2013.