#5876
Twice each year influenza experts gather to discuss recent developments in human and animal influenza viruses around the world, and to decide on the composition of the next influenza season’s flu vaccine.
Due to the time it takes to manufacture a vaccine, decisions on which strains to include must be made six months in advance.
The composition of the northern hemisphere’s vaccine is decided upon in February of each year, and decisions on the southern hemisphere’ vaccine are made in September.
Accordingly, last week representatives from divisions of the World Health Organization’s GISRS (Global Influenza Surveillance and Response System), along with members of OFFLU (the OIE/FAO Network on Animal Influenza), and other experts gathered in Chavannes-de-Bogis, Switzerland.
The agenda for this meeting (WHO Consultation on the Composition of Influenza Vaccine for the Southern Hemisphere 2012) states the following objectives:
1. Analyse the antigenic and genetic characteristics of influenza viruses circulating and infecting humans, taking into consideration of available epidemiological and clinical information from individual countries and regions;
2. Make recommendations on the composition of the influenza vaccines for use in the southern hemisphere 2012;
3. Review the antigenic and genetic characteristics of recent A(H5N1) viruses that the WHO Collaborating Centres of the WHO GISRS received and the need to develop new A(H5N1) candidate vaccine viruses for pandemic preparedness purposes;
4. Review the antigenic and genetic characteristics of other subtype influenza viruses, if any, infecting humans recently, and the need to develop new candidate vaccine viruses for pandemic preparedness purposes.
Below are some excerpts from their 15-page report: Recommended composition of influenza virus vaccines for use in the 2012 influenza season - full report
Zoonotic influenza infections caused by avian A(H5N1), avian A(H9N2) and swine A(H3N2) viruses
From 16 February 2011 to 19 September 2011, 45 confirmed human cases of A(H5N1), 24 of which were fatal, were reported by Bangladesh, Cambodia, Egypt and Indonesia, countries in which highly pathogenic avian influenza A(H5N1) is present in poultry. Since December 2003, a total of 564 cases with 330 deaths have been confirmed in 15 countries. To date there has been no evidence of sustained human-to-human transmission.
One human case of influenza A(H9N2) was detected in Bangladesh and four human infections caused by swine A(H3N2) viruses were detected in the United States of America during the same period.
Under the heading: Antigenic and genetic characteristics of recent isolates, the group found that despite growing diversity among variants of the 2009 H1N1 pandemic virus, the vast majority remain antigenically similar to the original virus.
Influenza A(H1N1) viruses
Between February and August 2011, all influenza A(H1N1) viruses detected worldwide were A(H1N1)pdm09; no former seasonal A(H1N1) viruses were detected. Haemagglutination inhibition (HI) tests using post-infection ferret antisera indicated that A(H1N1)pdm09 viruses remained antigenically homogeneous and closely related to the vaccine virus A/California/7/2009.
The same could be said for the H3N2 virus, where the majority of samples remain antigenically similar to the A/Perth/16/2009 virus which has been part of the flu vaccine for the past couple of years.
Influenza A(H3N2) viruses
The majority of A(H3N2) viruses collected from February to August 2011 were antigenically closely related to the vaccine virus A/Perth/16/2009. Antigenic characteristics were assessed with panels of post-infection ferret antisera in HI and virus neutralization assays. The HA genes of recent viruses fell into two phylogenetic clades represented by A/Perth/16/2009 and A/Victoria/208/2009, with the vast majority falling within the A/Victoria/208/2009 clade.
Influenza B is always a bit of a wildcard, since there are two main strains in circulation, and only one is currently included in the vaccine. In recent years the Victoria strain has been dominant, but the Yamagata lineage waits in the wings and continues to circulate in northern China.
Influenza B virusesInfluenza B viruses of both the B/Victoria/2/87 and the B/Yamagata/16/88 lineages co-circulated, with B/Victoria/2/87 lineage viruses continuing to predominate globally. However,in northern China, B/Yamagata/16/88 lineage viruses predominated from February to May 2011 before influenza activity declined.
The bottom line: The bulk of the influenza viruses currently circulating, while they continue to evolve, remain antigenically similar to to those that have been including in the flu vaccine since 2010.
When a strain is said to be `antigenically similar’ to the vaccine strain, it is expected (but not assured) that the vaccine remains reasonably effective.
While research and refinements in candidate vaccines continue, next year’s vaccine recommendations for the southern hemisphere remains essentially the same for the third year in a row.
The report concludes:
It is expected that A(H1N1)pdm09, A(H3N2) and B viruses will co-circulate in the 2012 southern hemisphere season.
It is recommended that the following viruses be used for influenza vaccines in the 2012 influenza season (southern hemisphere):
– an A/California/7/2009 (H1N1)pdm09-like virus;
– an A/Perth/16/2009 (H3N2)-like virus;
– a B/Brisbane/60/2008-like virus.
Flu viruses are constantly changing, mutating, and evolving making any forecast a bit of a gamble. As we saw with the 2009 H1N1 swine flu, a novel virus can emerge and change the viral landscape practically overnight.
But despite the variability and unpredictability of influenza, the track record for selecting influenza A strains for the flu shot has actually been pretty good over the years.
We won’t know how well this decision will turn out in the southern hemisphere for another 6 to 12 months, but for those of us north of the equator, this is a pretty good indication that confidence in the makeup of this fall’s flu vaccine remains high.
A good enough reason to go ahead and get the shot this year, before flu season arrives.
