Duration of immunity induced by an adjuvanted and inactivated equine influenza, tetanus and equine herpesvirus 1 and 4 combination vaccine.

This study investigates the effectiveness and longevity of immunity provided by a combined vaccine for equine influenza, tetanus and equine herpesvirus 1 and 4 in young foals. It revealed high-level, long-term immunity against the diseases, demonstrating similar efficacy to monovalent vaccines.

Study Design and Groups

• The research involved the administration of a combined vaccine to two groups of foals. The vaccine included inactivated equine influenza, herpesvirus antigens, and tetanus toxoid. Group A received this combined vaccine.
• The first two doses of the vaccine were given four weeks apart and the third was given six months later.
• Another set of foals, Group B, were given a monovalent equine herpesvirus (EHV) vaccine, EHV1.4, on the same schedule.
• Four and a half months after the third vaccination of Groups A and B, a third group, Group C, was injected twice with the monovalent EHV1.4 vaccine, four weeks apart.
• There was also an unvaccinated control group, Group D.

Vaccine Effects on Antibodies

• The researchers examined the antibody responses from the foals’ first vaccination until one year after their third vaccination.
• High antibody titers, which indicate strong immunity, were observed two weeks after the second vaccination with the combined vaccine.
• These titers decreased until the third vaccination, after which they rapidly increased again and remained high for at least a year.
• Antibody titers against tetanus peaked after the third vaccination but remained high enough to offer protective immunity for at least a year.
• Foals vaccinated with the monovalent EHV1.4 vaccine (Group B) remained without antibodies for influenza and tetanus throughout the study.

Comparison of Vaccines

• Two weeks after the second dose of the monovalent EHV1.4 vaccine was administered to Group C, all groups (including the unvaccinated group D) were exposed to EHV-4.
• The vaccinated foals (Groups A, B and C) showed a significant reduction in clinical symptoms and virus excretion compared with the unvaccinated foals.
• There was no noticeable difference between the vaccinated groups, which suggests that the combined vaccine protects as well as the monovalent vaccine.

Conclusions

• The combined vaccine induced clear protection up to six months after vaccination, similarly to the EHV1.4 vaccine. Based on these findings, the researchers conclude that the efficacy of the combination vaccine against EHV-1 challenge is likely similar to the efficacy induced by EHV1.4 vaccination.