During 2011, outbreaks/cases of equine influenza were reported by France, Germany, Ireland, Mongolia, Sweden, United Kingdom (UK), and United States of America (USA).
Equine influenza A (H3N8) viruses were isolated and/or characterised from outbreaks in France, Germany, Ireland, the UK and the USA.
Equine influenza virus infections were confirmed in vaccinated and unvaccinated horses. Vaccination breakdowns were observed in training yards in France and Germany and in an equestrian centre in Germany. The viruses identified belonged to clade 2 of the Florida sublineage. Horses regularly vaccinated with different vaccines, including vaccines updated according to the 2004 recommendations to incorporate an A/eq/South Africa/04/2003-like virus, were affected. These vaccines had not been updated in accordance with the recommendations of 2010 and 2011, to include a virus from clade 2 for optimum protection.
A clade 1 virus of the Florida sublineage was isolated from a regularly vaccinated horse at the Belmont training track in New York.
Fatalities associated with influenza infection were reported in France and Mongolia.
Viruses isolated/identified in 2011 from four outbreaks in France, two outbreaks in Germany, two outbreaks in Ireland, seven outbreaks in the UK and three in the USA were characterised genetically by sequencing of the haemagglutinin (HA) gene. Viruses isolated in the UK and in the USA were also characterised antigenically by haemagglutination inhibition (HI) assay using post-infection ferret antisera.
All HA1 sequences obtained from viruses were of the American lineage (Florida sublineage). The viruses identified in France, Germany, Ireland and the UK were characterised as clade 2 viruses. The viruses identified in the USA were characterised as clade 1 viruses. New HA amino acid substitutions were seen in viruses of both sublineages compared with isolates from 2010, further increasing the sequence divergence between the sublineages.
HI data and antigenic cartography analysis of HI data available for viruses isolated in 2011 indicate that the two clades of the Florida sublineage continue to evolve.
No Eurasian viruses were isolated in 2011. The majority of the viruses isolated and characterised were from the American clade 2 lineage (Florida sublineage). Only viruses isolated in the USA fell within clade 1. There was evidence of a lack of vaccine efficacy, particularly against clade 2 viruses.
The panel continues to emphasise the importance of increased surveillance and investigation of vaccination breakdown in different countries. Rapid submission of viruses to reference laboratories is essential if antigenic and genetic drift is to be monitored effectively on a global basis.
Vaccines should contain epidemiologically relevant viruses.
The updating of vaccines in a timely manner is necessary for optimum protection.
It is not necessary to include an H7N7 virus or an H3N8 virus of the Eurasian lineage in vaccines as these viruses have not been detected in the course of recent surveillance and are therefore presumed not to be circulating.
Vaccines for the international market should contain both clade 1 and clade 2 viruses of the Florida sublineage.
Clade 1 is represented by A/eq/South Africa/04/2003-like or A/eq/Ohio/2003-like viruses.
Clade 2 is represented by A/eq/Richmond/1/2007-like viruses.
A panel of viruses covering both clades is available from the OIE Reference Laboratories.
Manufacturers producing vaccines for a strictly national market are encouraged to liaise with Reference Laboratories. This will ensure utilisation of reference reagents in the selection of viruses for inclusion in vaccines that induce cross-reactive responses that are immunogenically relevant to the equine influenza viruses circulating nationally.
Freeze-dried post-infection equine antisera to A/eq/Newmarket/1/93 (American lineage H3N8) and A/eq/South Africa/4/2003 (Florida clade 1, sublineage of the American lineage) are available from the European Directorate for the Quality of Medicines (EDQM). These sera have been assigned Single Radial Haemolysis values through an international collaborative study and can be used as primary reference sera for the assay.