Safety, efficacy, and immunogenicity of a modified-live equine influenza virus vaccine in ponies after induction of exercise-induced immunosuppression.

This study investigates the safety, effectiveness, and immune response of an intranasal cold-adapted modified-live equine influenza virus vaccine given to ponies, after they had been exposed to strenuous exercise that induced an immune response. It found the vaccine to be safe and protective, even in ponies with temporary immune suppression due to physical activity.

Experiment Design and Methodology

• The researchers ran a prospective study involving fifteen young ponies, aged between 9 to 15 months that had no prior exposure to influenza.
• Five ponies were subjected to five days of strenuous exercise then vaccinated, another five were only vaccinated, and the remaining five neither conducted exercise nor were vaccinated – they acted as the control group.
• Three months post-vaccination, all the ponies were exposed to an equine influenza virus in a standardized manner through nebulization.
• The researchers kept a close watch on the clinical signs, blood results, virus shedding in vaccinated and control horses. They also collected serum and nasal secretions to evaluate antibody isotype responses specific to the influenza virus.

Results

• Exercise was found to cause a degree of immunosuppression in the ponies, as evidenced by a decrease in lymphocyte proliferation in reaction to pokeweed mitogen.
• Vaccination did not result in any adverse clinical effects. Also, none of the vaccinated ponies presented any clinical signs of infection after exposure to the virus.
• On the other hand, four out of five control ponies presented distinct clinical signs of respiratory disease following exposure.
• Both vaccinated and control ponies shed the virus after exposure. However, vaccinated ponies were clinically healthy despite this fact.
• Antibody response to the vaccine was similarly observed in serum IgGa and IgGb responses in both groups of vaccinated ponies. After being exposed to the virus, all ponies generated similar serum IgGa and IgGb as well as nasal IgA responses.
• The pattern of serum hemagglutination inhibition titers, a test used to measure the level of influenza antibodies, mirrored the patterns of IgGa and IgGb responses.

Conclusions

• The study results suggest that modified-live equine influenza vaccine administered to ponies, even during a period of exercise-induced immunosuppression, is safe. Moreover, a single dose was shown to provide clinical protection 3 months later.