Duration of tetanus IgG titres following basic immunisation of horses

Reasons for performing study:

Recommendations for prophylactic vaccination against tetanus in horses vary greatly between countries and have scarce scientific support in the peer-reviewed literature. In human medicine, recommended booster vaccination intervals are also very variable, but are considerably longer than for horses.

Objectives:

To investigate if the duration of antibody titres previously determined to be protective against tetanus are likely to be longer than indicated by several recommended vaccination intervals for horses.

Study design:

Prospective clinical trial.

Methods:

Thirty-four horses were enrolled for basic immunisation with an ISCOM Matrixcombination vaccine (Equilis® Prequenza TE). Horses received the first vaccination at 5–11 months of age, and the second dose 4 weeks later. A third vaccine dose was given 15–17 months after the second dose. Serum tetanus antibody titres were analysed by ToBi ELISA 2 weeks as well as 14–16 months after the second dose. After the third vaccine dose, titres were checked once yearly for 3 years.

Results:

Two weeks after the second dose all horses (34/34) had antibody levels that exceeded 0.03 iu/ml. After 16 months the levels were below 0.03 iu/ml in 5/33 horses. After the third vaccine dose antibody levels remained above 0.03 iu/ml in 25/26 horses for 1 year, 17/17 horses for 2 years, and 9/9 horses for 3 years.

Conclusions:

Horses that undergo basic immunisation with 3 doses of vaccine after the age of 6 months are likely to have serum antibody titres consistent with protection against tetanus for more than 3 years