Andrew Easton, Professor of Virology at the University of Warwick, has commented on the World Health Organisation's (WHO) decision on the composition of the 2015-16 influenza vaccine for the northern hemisphere:
On the composition of the influenza vaccine for 2015-2016:
“The WHO has concluded the assessment of the four candidate influenza viruses that will be used in the vaccines for use in the winter of 2015. As with every year, the WHO convenes a meeting to consider the strains of influenza that have been detected most frequently over recent months. This information is used to make the best estimate of the strains most likely to be prevalent in the next winter season, which are then incorporated into the approved vaccine formulation that companies will now begin to produce. This advance prediction is necessary to allow companies the necessary time to scale up production and ensure that sufficient vaccine is available at the beginning of the next influenza season.
“Historically the assessment of which strains to use in the vaccine has been successful despite the planning situation being similar to aiming at a moving target whose direction and speed you cannot predict. As a result there is inevitably an element of risk as the influenza virus can mutate at a rapid rate which means that by the start of the winter season it can be sufficiently different to the strain detected earlier in the year that the vaccine does not work as well as desired. In the formulation for this year one of the strains, called H3N2, used for the vaccine had mutated much more rapidly than anticipated in the period between the decision for its inclusion and use of the vaccine, with the result that there was a poor match between the vaccine strain and the strain infecting people. The remaining 3 strains in the vaccine were good matches but unfortunately the H3N2 virus was the predominant one seen in the winter season for 2014/15.
“The WHO considerations just concluded will include an assessment of the events of recent months but, as with any such system, it is only possible to make the best estimate on the evidence available. Despite concerns, the formulations of influenza vaccines over the years have been successful in preventing large numbers of infections and have reduced deaths in the high risk groups in the population such as the elderly.”
On the WHO report, ‘Warning signals from the volatile world of influenza viruses’:
“All influenza viruses that infect humans originated in other species from where they spread into the human population. The greatest diversity of influenza A virus strains is seen in aquatic birds and it is from these, possibly combined with flu strains present in other animals such as pigs, that human infections have arisen. The introduction of new influenza strains into humans from animals has generated worldwide pandemics which have been devastating in terms of the numbers of people seriously affected or killed. Fortunately, animal influenza viruses do not easily make the transition into new species such as humans so many of the viruses fail to find a foothold and so despite causing small-scale outbreaks do not become established as common infections with potentially devastating consequences.
“As analytical techniques have improved we have been able to identify the scale of diversity of influenza viruses present in wild animals that may pose a threat. At the same time our surveillance skills have improved and we can now rapidly identify the relatively small-scale outbreaks of animal influenza virus infections in humans. Laboratory experiments, some of which have been controversial, have focused on identifying the mutations in influenza viruses that are required to give the virus the best characteristics for infection in humans. All of these elements have provided us with the information necessary for identifying potential threats from animal flu.
“This report has particularly highlighted H5N1 influenza virus strains as a potential pandemic risk due to the very high death rate associated with infection. However several other influenza virus strains have also been seen to cross over from animals into humans and cause fatal infections, though on a smaller scale than for H5N1. It is not possible to predict with certainty which animal influenza strain will cause the next pandemic, though we can be certain that one will. It is therefore essential that we maintain as strong a surveillance system as possible to identify new human infections and to track the course of any such infections when they occur. This will provide us with the best opportunity to be able to respond when a new virus is able to establish itself as an efficient infection of humans.”