High rates of vaccination among France’s 1.1 million horses against equine influenza appear responsible for the country’s low rate of infection, research shows.
In fact, no cases of equine influenza were identified in French horses between 2015 and late 2018, based on reporting to the French equine infectious diseases surveillance network.
Stéphanie Fougerolle and her colleagues discussed the use of vaccination against the virus in a recent issue of the journal Vaccines.
The study team said vaccination against the equine influenza virus remains one of the most effective methods to prevent or limit outbreaks.
They considered that the lack of detection of the pathogen in France — which is home to 15% of Europe’s horses — could be linked to high vaccination coverage.
The researchers set out to evaluate immunity and vaccine coverage in the country through a large-scale serological study.
A total of 3004 archived surplus serum samples from French horses of all ages, breeds and sexes were selected from four different geographical regions. They had been collected for a variety of purposes, such as pre-sale health checks, export requirements, breeding and illness.
The samples were analysed to find evidence of an antibody response to the flu virus using two methods.
Overall immunity coverage against equine flu was found to be 87.6% among the sampled horses.
For comparison, studies that have investigated vaccination coverage in humans against influenza indicate coverage that is often below 60%.
One of the tests was able to distinguish between the antibody response from horses that had actually had a bout of the flu from that generated by the vaccine. The evidence suggested that the great majority of the detected antibody response arose from vaccination (a recombinant canarypoxvirus-based EI vaccine is mostly used in France).
The findings, they said, supported the absence of equine flu virus circulation in French horses between 2015 and late 2018.
“Results from this study confirm a strong equine influenza immunity in a large cohort of French horses, which provides an explanation to the lack of clinical equine influenza in France in recent years and highlights the success of vaccination against this disease,” the study team wrote.
However, this protection has been challenged since December 2018, with the incursion in Europe of a Florida Clade 1 sub-lineage of equine flu virus, undetected in France since 2009.
There have been many outbreaks reported in several European countries (Belgium, Germany, Ireland, the Netherlands, Sweden and Britain). The scale, number and duration of this epidemic has not been experienced in Europe since the late 1970s and 1980s.
Before this, the last French equine flu outbreaks had been reported in 2014 and 2015 but were limited in size and number (just six horses in one outbreak and four in the other).
“Other European countries with large equid populations report equine influenza cases every year,” the authors noted.
It would be interesting, they said, to determine the extent of vaccination coverage in those countries.
The researchers said their results had significance for both equine veterinarians and the scientific community.
“When extrapolated to a country level, they highlight the success of equine influenza vaccination and are concomitant with a lack of detection of the pathogen and an absence of clinical equine influenza in the horse population in France.”
This information is particularly timely, they said, because the French horse population suffered from an extended outbreak of equine herpesvirus infection in early 2018, which could be an indirect consequence of a nationwide equine herpesvirus vaccine shortage in 2016, and potential modification of vaccination habit and coverage against this specific pathogen in 2017.
“As a result, this study and results could inspire equine veterinary practitioners and horse owners to continue and intensify their effort in terms of vaccination.”
While vaccine coverage in France is challenged by this latest equine flu strain, the benefit of immunization in easing disease severity and reducing the rate of transmission remains clear.
Further work is warranted, they said, to explain this year’s flu epidemic in France.
The study team comprised Fougerolle, Christine Fortier, Loïc Legrand, Marion Jourdan, Christe Marcillaud-Pitel, Stéphane Pronost and Romain Paillot, from a range of French institutions.
Success and Limitation of Equine Influenza Vaccination: The First Incursion in a Decade of a Florida Clade 1 Equine Influenza Virus that Shakes Protection Despite High Vaccine Coverage
Stéphanie Fougerolle, Christine Fortier, Loïc Legrand, Marion Jourdan, Christe Marcillaud-Pitel, Stéphane Pronost and Romain Paillot.
Vaccines 2019, 7(4), 174; https://doi.org/10.3390/vaccines7040174