Serologic responses to eastern and western equine encephalomyelitis vaccination in previously vaccinated horses.

The study investigates how horses, which had already been immunized, react to a further round of vaccines against Eastern and Western equine encephalomyelitis (EEE and WEE). Findings show that post-vaccination immune responses are variable, with some horses having low or untraceable antibodies even six months after vaccination.

Research Objective

• The research aimed at understanding the serologic (relating to the serum component of blood) responses of horses previously vaccinated against EEE and WEE, to revaccination against both diseases.

Methodology

• This was a prospective study, meaning the researchers followed the subjects over a period to observe the effects of the revaccination.
• Scientists monitored the response of each horse towards each antigen (toxin or foreign substance that induces an immune response) involved in the vaccination.

Findings

• The study found the horses’ response to be variable after revaccination. That is, the horses reacted differently to the vaccines – some had a strong immune response while others had a weaker one.
• In some cases, the horses did not show any increase in titers (concentration of antibodies) against EEE or WEE even after being recently vaccinated. This indicates a lack of or a weak immune response to vaccination.
• To further stress this point, some horses had low or even undetectable levels of antibodies six months after vaccination.
• Overall, the geometric mean (statistical measure) of titers peaked 2 weeks after the revaccination, and this represented a significant increase from the pre-revaccination levels.
• As an exception, in one horse, the EEE:WEE titer ratios varied between 0.25 to 2.0.

Implications

• The study showed regular EEE and WEE vaccinations did not interfere with testing for another horse disease, Saint Louis encephalitis. This indicates that multiple vaccinations can be administered together without impacting the effectiveness of each other.
• These findings can help veterinary practitioners understand the immunization process against EEE and WEE and determine the best vaccination schedules for horses.