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Equine influenza

OIE Expert Surveillance Panel on Equine Influenza Vaccine Composition, OIE Headquarters, 6 March 2015

Conclusions and Recommendations

• Influenza activity in 2014

During this period, individual animal cases and outbreaks of equine influenza were reported by France, Germany, Ireland, Sweden, the UK and the USA.

• Sources of viruses characterised during 2014

Equine influenza A (H3N8) viruses were isolated and/or characterised from outbreaks in all the countries listed above.

• Field data

Equine influenza virus infections were confirmed in both vaccinated and unvaccinated horses. In 2014 there was an increase in influenza activity in Europe particularly in the UK and Ireland with cases confirmed on 31 and 18 premises respectively. The majority of the clinically affected horses were unvaccinated or of unknown vaccination history, but vaccination breakdown was recorded in several racing yards in Ireland. Equine influenza outbreaks were confirmed on 28 premises in 19 states in the USA. The vaccination history was unknown in the majority of cases but vaccination breakdown was recorded in a boarding facility in Tennessee.

• Characterisation of viruses isolated in 2014

Viruses isolated/identified from outbreaks in France, Germany, Ireland, Sweden, the UK and the USA were characterised genetically by sequencing of the haemagglutinin (HA) gene. The sequences of the neuraminidase (NA) genes for several virus isolates from Ireland, Sweden, the UK and the USA were determined.  Viruses isolated in Ireland, the UK and the USA were also characterised antigenically by the haemagglutination inhibition (HI) assay using post-infection ferret antisera and chicken red blood cells.

• Genetic characterisation

All HA sequences obtained from viruses were of the American lineage (Florida sublineage).  The viruses detected in the USA, were characterised as clade 1 viruses. Viruses detected in France, Germany, Ireland, Sweden and the UK were characterised as clade 2 viruses.

Two subpopulations of clade 2 viruses have been identified with amino acid substitutions in HA1 at either position 144 or position 179. The majority of 2014 viruses characterised had a valine at position 144 and an isoleucine at position 179. No equine influenza viruses were identified in Asia in 2014, but clade 2 viruses from Asia are distinguishable from those circulating in Europe.

The NA gene sequences of viruses from clade 1 and clade 2 were clearly distinguishable.

Representative sequences for HA and NA are available on GenBank and GISAID.

• Antigenic characteristics

HI data available for viruses isolated in 2014, and antigenic cartography analyses thereof, show that the two clades of the Florida sublineage continue to co-circulate and evolve but currently remain antigenically closely related to the recommended vaccine viruses of that lineage.

• Conclusions

No Eurasian viruses were detected in 2014.  Viruses isolated and characterised were from clades 1 and 2 of the Florida sublineage. Viruses of both clades were associated with vaccination breakdown.

• Level of surveillance and updating of vaccines

The panel continues to emphasize the importance of increased surveillance and investigation of vaccination breakdown in different countries. Increased surveillance in Asia has been facilitated by the OIE Twinning programme.  Rapid submission of viruses to reference laboratories is essential if antigenic and genetic drift is to be monitored effectively on a global basis.

Although some vaccines have been updated to include a virus from clade 2, in accordance with the recommendations of 2010 to 2014, the majority of current vaccines contain outdated strains.

The updating of vaccines with epidemiologically relevant viruses is necessary for optimum protection. The panel welcomes the replacement of the EMA   Note for Guidance on the Harmonisation of requirements for equine influenza vaccines – Specific requirements for substitution or addition of a strain or strains (EMEA/CVMP/112/98-FINAL) with the Guideline on Data Requirements for Changes to the Strain Composition of Authorised Equine Influenza Vaccines in line with OIE recommendations (EMA/CVMP/IWP/97961/2013) and any amendments to regulatory procedures that allow equine influenza vaccines to be updated as speedily as possible without compromising safety and efficacy.

• Recommendations

These are unchanged from those made in March 2014.

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 the most 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. Recent clade 1 viruses are available from the OIE reference laboratories.

Clade 2 is represented by A/eq/Richmond/1/2007-like viruses. Recent clade 2 viruses are available from the OIE reference laboratories.

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.  The selected viruses should induce responses which are immunogenically relevant to the equine influenza viruses circulating nationally. Sequence determination of both HA and NAs should be completed before use.

• Reference reagents

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. There is no SRH reference serum available currently for A/eq/Richmond/1/2007, representative of Florida clade 2. The need for such a reference serum is recognised by the panel.

There is currently a shortage of standardised antigen for the purpose of quantifying HA. Single Radial Diffusion reagents will no longer be produced by the National Institute for Biological Standards and Control (NIBSC). Vaccine companies should inform the OIE if there is a need for updated SRD reagents or other standards.

Recent virus strains, including suitable vaccine candidates for clades 1 and 2, are available from the OIE reference laboratories. In the event that an OIE reference laboratory cannot supply suitable vaccine candidates for both clades, they will assist the vaccine company to source the viruses from an alternative OIE reference laboratory.

Small quantities of ferret antisera for antigenic characterisation are available from the OIE reference laboratories in the UK and Ireland.

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