Optimising vaccination strategies in equine influenza.

This study investigates the potential impact of altering vaccination strategies for equine influenza in Thoroughbred racehorses. The researchers used a complex mathematical model and real-world data to suggest that increasing the frequency of vaccination in older horses could significantly reduce the risk of an outbreak.

Creation of the Stochastic Model

• The research team used a stochastic model, a kind of mathematical equation that includes random variables, to simulate the spread of equine influenza in a hypothetical Thoroughbred training yard.
• The model incorporated information about the duration of the latent (non-infectious) and infectious periods of the disease, derived from experiments carried out by the Animal Health Trust.
• Data from previous equine influenza epidemics were also included to estimate the rate at which the disease might spread among horses.

Establishing a Relationship Between Antibodies and Infection Probability

• The team worked with 89 ponies to establish a relationship between the level of antibodies (which fight disease) in the horses’ systems prior to exposure to the flu virus and the likelihood of the horses becoming infectious.
• To accomplish this, the researchers used a statistical method called logistic regression, which can describe and test relationships between a binary outcome (in this case, becoming infectious or not) and one or more predictive variables (in this case, pre-challenge antibody level).

Assessing the Risk of an Equine Influenza Outbreak Under Current Vaccination Policies

• Using this model, the researchers studied a plausible Thoroughbred population over a year to assess the risk of an equine influenza outbreak under the current minimum vaccination policy in the UK.
• The team also examined changes in antibody level over time, incorporating data from both published and unpublished studies including 618 ponies and horses.

Assessment of Alternative Vaccination Strategy

• The model was then adapted to consider a different vaccination programme, in which older horses (aged two years and upward) would receive vaccinations more frequently.
• The modified model showed that this alternative approach could significantly increase the protection against equine influenza among the population of racehorses studied.

Assessment of Secondary Outbreak Risks

• The team also evaluated the potential for the disease to spread from one yard to another, aiming to determine the risk of secondary outbreaks.