CORE VACCINATIONS:
Protection from diseases that are endemic to a region, those with potential public health significance, required by law, highly infectious, or pose a risk of severe disease and death.
RISK-BASED VACCINATIONS:
Protection from diseases which your horse may be more likely to encounter depending on where you live, your travel plans, and amount of socialization selected for use based on risk assessment performed by, or in consultation with, a licensed veterinarian.
KEYWORDS
horse, adverse, hesitancy, influenza, outbreak, vaccination
INTRODUCTION
Vaccination is an integral component of preventive medicine in equine practice. Equine vaccination is most commonly performed against equine influenza (EI) and tetanus, with an owner-based survey reporting 71.3% horses were vaccinated for both EI and tetanus in Great Britain1 with lower vaccination rates in ponies, retired and companion animals. This study, however, is likely to be an overestimation due to respondent bias, and although sufficient data in this area are lacking, crude estimates which take into account vaccine manufacturer sales and the estimated horse population in the United Kingdom (UK) give an approximate figure of only 30% horses that are vaccinated (R. Newton, personal communication, 2020).
There are multiple sources of guidance and regulations on equine vaccination in the UK, particularly for EI; including various competition, riding club and racing rules,2-4 in addition to organisations including the World Health Organisation for Animal Health (OIE).5 With outbreaks of EI, and equine herpes virus (EHV) in the UK in 2019, the effectiveness of vaccination continues to be under closescrutiny. Equiflunet,7 a free online disease surveillance tool created by the Animal Health Trust, reported 228 laboratory confirmed outbreaks of EI in 2019, most of which affected multiple horses.
Equine Influenza vaccine practices
Respondents’ recommendations for the age of first vaccination ranged from 6 weeks to 4 years old. The most commonly recommended age for starting vaccination was from 6 months old. 97.4% (n = 296/304; 95% CI 94.9%-98.7%) respondents advised the same age of first vaccination for both competing and noncompeting animals. For the first vaccination age, 89.1% (n = 271/304; 95% CI 85.1%-92.2%) of responses were compliant with datasheet recommendations in competition horses, and this was similar in noncompetition horses (89.5%, n = 272/304; 95% CI 85.5%-92.4%). The most common reason for noncompliance was vaccinating earlier than 6 months with the Equilis Prequenza (MSD Animal Health) product. Across all products used, 29.6% (n = 90/304; 95% CI 24.8%-35.0%) respondents’ recommended protocols where first vaccination could be initiated in animals under 6 months of age. (Equilis Prequenza, MSD Animal Health is licensed for use from 4 months in foals with an insufficient colostrum intake, however, the datasheet recommends restarting a primary course at 6 months in this instance.) Respondents’ recommendation for first to second vaccine interval ranged from 21 days to a maximum of 95 days. The most common interval stated was 21-92 days for both competing and noncompeting horses, recommended by 42.7% (n = 128/300; 95% CI 37.2%-48.3%) of respondents for competition horses and 41.7% (n = 125/300; 95% CI 36.2%-47.3%) for noncompetition horses.
Vaccine hesitancy
The majority (86.4%, n = 261/302; 95% CI 82.1%-89.8%) of respondents had encountered some aspect of vaccine hesitancy or reluctance to vaccinate from owners. When asked to describe the frequency of encountering vaccine hesitancy, 298/304 of the survey participants responded, of whom 57.5% (n = 150/298; 95% CI 44.7%- 56.0%) encountered it rarely (less than annual), 45.6% (n = 119/298; 95% CI 34.5%-45.6%) encountered it sometimes (less than monthly) and 11.1% (n = 29/298; 95% CI 6.9%-13.6%) encountered it often (more than monthly). The most common reasons for vaccine hesitancy in horse owners encountered by respondents were as follows unnecessary need of vaccination.
Change in practice following 2019
EI outbreak
Of the respondents, 63.2% (n = 192/304, 95% CI 57.6%-68.4%) had permanently changed their practice following the 2019 EI outbreak, 18.8% (n = 57/304, 95% CI 14.8%-23.5%) had changed their practice temporarily and resumed previous practice and 18.1% (n = 55/304, 95% CI 14.2%-22.8%) had not changed their practice. Of those who changed their practice; 97.2% (n = 242/249, 95% CI 94.3%-98.6%) changed frequency of administration, with 57.4% (n = 139/242, 95% CI 51.1%-63.5%) of those changing to 6 monthly ‘booster’ vaccination, 10.4% (n = 26/249, 95% CI 7.2%-14.9%) changed brand of vaccination and 3.6% (n = 9/249, 95% CI 1.9%-6.7%) used different antigens most commonly by incorporating EI vaccination into protocols for geriatric/unridden animals.
