Risk factors for influenza infection in vaccinated racehorses: lessons from an outbreak in Newmarket, UK in 2003.

The research looks into the risk factors for influenza in vaccinated racehorses during an outbreak in the UK in 2003. The study found that younger horses were less susceptible to infection despite similar antibody levels to older horses, potentially due to recent vaccination. The research also found evidence of gender influencing susceptibility and suggested potential negative effects from early vaccination in the presence of maternal antibodies.

Overview of the Study

• The research was triggered by an outbreak of clinical equine influenza in vaccinated racehorses in Newmarket, UK from March to May 2003.
• The study focused on examining the risk factors for the infection, particularly why 2-year-old horses were less susceptible than older animals.

Findings of the Research

• The study made several key findings. The primary discovery was the lower susceptibility of 2-year-old horses to the influenza infection compared to older horses. The decrease in susceptibility was mainly attributed to more recent vaccination in younger horses, despite the antibody levels between different age groups being similar overall.
• The researchers also found that there could be a sexual dimorphism in susceptibility to the infection, although the actual differences and reasons behind these potential sex-based variations were not specifically detailed.
• Another significant finding was the possible negative effects of vaccination at a young age when maternal antibodies are present. This suggests that the timing of vaccination could have far-reaching impacts on long-term immunity to the influenza infection.

Implications of the Research

• An interesting implication of the study is the support it gives to the practice of blanket vaccination soon after initial diagnosis, often termed as ‘vaccinating in the face of the outbreak.’ This could be a useful method of controlling future outbreaks.
• The research also indicated that the protective immunity offered by vaccines with only aluminium hydroxide as the adjuvant might be sub-optimal compared to other vaccines. It implies a need to examine and potentially reconsider the composition of vaccines used for equine influenza.