Evaluation of Three Different Vaccination Protocols against EHV1/EHV4 Infection

Protocol G3 (4 doses of a inactive EHV1/4 vaccine) gave superior titers of antibodies to the EHV virus. None in any of the groups, including the controls experienced abortion leaving the meaning of the titers unknown. However other mares not participating in the trial did have abortions. Further work needs to be done to assess the meaning of this and, as this is the best look at different Herpes abortion protocols I have seen, in the mean time I would consider using protocol G3 for mares at risk.
DrO

Evaluation of Three Different Vaccination Protocols against EHV1/EHV4 Infection in Mares: Double Blind, Randomized Clinical Trial
Anna-Rita Attili 1, Renato Colognato 2, Silvia Preziuso 1, Martina Moriconi 1 3, Silvia Valentini 4, Stefano Petrini 5, Gian Mario De Mia 5, Vincenzo Cuteri 1

Abstract
EHV1 and EHV4 are the most important herpesviruses in horses. Repeated cases of abortion in mares regularly vaccinated, prompted us to investigate the immune response after vaccination with the same inactivated vaccine, but with three different protocols. Eighteen mares were chosen and randomly divided in three study groups (G1-G2-G3) and a control group (Ctrl).

All the mares were injected with the same inactivated vaccine prepared with 438/77 EHV1 strain and 405/76 EHV4 strain and Carbopol 934P as adjuvant. G1 received the immunization at the third, fifth and seventh month of pregnancy; G2, at the fifth, seventh and ninth month of pregnancy as suggested by the Manufacturer; G3, 7 days before the expected date of birth (days before delivery, DBD) and at the first, fourth and sixth month of pregnancy. The Ctrl group have, instead, received sterile saline placebo at fifth, seventh and ninth month of pregnancy. The 2 mL vaccine dose and placebo were administered intramuscularly (IM) on the left side of the neck.

For serologic and PCR investigations nasal swabs, sera and blood were collected. The protocol used in G3 (4 doses) increased the titer recorded by ELISA and seroneutralization (SN). Poor agreement and no correlation were observed in titer values between ELISA and SN and between SN and PCR. A very weak positive correlation between ELISA and PCR was obtained. Seven out of 18 nasal swabs were positive by PCR; none showed viremia and no abortion occurred, regardless of vaccination status and despite active circulation of EHV-1 in the farm at the time of the study. The study was conducted in field conditions, in a susceptible population with a known history of infection and abortion, and among the three protocols, the one proposed in the G1 was the least efficient while the one proposed for the G3, seems to have induced a higher antibody titer in both SN and ELISA.