The Effects of Biannual Equine Influenza Vaccine on Performance in Adult Horses

a Knowledge Summary by

Emma Shipman BVetMed, MSc, DipACVIM, CertVA, MRCVS^1*

¹School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington Campus, Leicestershire, LE12 5RD
^*Corresponding Author (emma.shipman@nottingham.ac.uk)

The evidence

There is no retrospective or prospective evidence examining performance in three day event horses after annual or biannual booster vaccination against equine influenza virus. There is no evidence examining performance levels in three day event horses after booster vaccination against equine influenza virus. There is a small amount of evidence, and the quality of the evidence is low, evaluating clinical and clinicopathological data that may relate to performance in adult warmblood horses undergoing booster vaccination and subsequent exercise. These five randomised controlled trials were conducted at one veterinary teaching hospital using a small number of adult warmblood horses over an 11 year period. The evidence evaluated may not be applicable outside the experimental group of 15 horses and some horses may have been included in more than one of the studies.

Summary of the evidence

Appraisal, application and reflection

There is no evidence available comparing performance levels in three day event horses receiving either biannual or annual booster vaccinations against equine influenza virus. There is no evidence available evaluating performance levels in three day event horses receiving booster vaccination for equine influenza virus or placebo controls.

Only low quality evidence is available from a group of five papers from one veterinary teaching hospital evaluating a variety of physical and clinicopathological variables in adult warmblood horses after either booster vaccination against equine influenza virus and equine herpes virus and rest or booster vaccination followed by a controlled exercise program for 4 days commencing 14 days after vaccination. Variables evaluated included:

• heart rate*, respiratory rate* and total red blood cell count *
• Serum proteins (albumin*, alpha 1, alpha 2*, beta 1* and beta 2*, gamma globulins)
• Fibrinogen*, haptoglobin erythrocyte sedimentation rate
• Total white blood cell, eosinophil, neutrophil* and lymphocyte* counts
• Lysozyme*, classical and alternate complement activation*

Statistically significant differences (P < 0.05) were noted in the above variables (*) at intermittent time points in the 14 days post exercise (corresponding to 18–31 days post booster vaccination.) Values were reported as means in all cases with mean plus standard error of mean in some publications. Confidence limits were not reported in any of the studies. Reported values remained within the published reference ranges for the conducting laboratories at all time points when these were reported in the studies. While the above variables are commonly evaluated in horses with reduced performance, athletic performance was not directly evaluated. The study participants were reported as male , male entire geldings or not reported and previous level of fitness prior to study inclusion was not discussed in any study. In all trials an exercise period of 4 days was used, which is likely to vary greatly to training programs for competing three day event horses. While all study horse were reported as being previously vaccinated for equine influenza virus and equine herpes virus 1&4 a year prior to inclusion in the trial, whether this was a booster or primary vaccine course was not discussed. All trials involved booster vaccination with an oil adjuvanted intramuscular vaccine and therefore these finding may not be relevant to horses receiving intranasal/immune stimulating complex (ISCOM) vaccines/vaccines containing varying influenza strain or vaccines containing equine influenza only.

Conclusions:

There is no evidence that biannual equine influenza vaccination compared to annual booster vaccination is associated with reduced performance in three day event horses. The quality of the data in adult warmblood horses in the 28 days period post booster vaccination where exercise occurred on days 14–17post vaccination is insufficient to determine whether athletic performance was affected during this period. More definitive conclusions on vaccination protocols in three day event horses cannot be drawn until higher quality evidence is available on the topic.

Methodology Section

Search Strategy
Databases searched and dates covered:	PubMed NCBI Platform 1973–2018 Week 16 CAB Abstracts on OVID Platform 1973–2018 Week 16
Search terms:	PubMed equine* or horse* or equus or equid* or mare or mares or pony or ponies or exp equidae/ or exp equus/ or exp horses/ or exp mares/ 'three day event*' or 'show jump*' or dressag* or endur* or exercis* or sport* or compet* or athlet* or 'cross country' exp show jumping/ or exp horse riding/ (1 and 2) or 3 vaccin* or immunisation or immunization or inoculation or exp vaccination/ or exp immunization/ influenza or flu or exp influenza/ 4 and 5 and 6 CAB Abstracts equine OR horse OR mare OR mares OR broodmares OR pony OR ponies three day evening OR show jumping OR dressage OR endurance OR exercise OR sport OR sporting OR competition OR athlete OR athletic OR cross country influenza OR flu vaccine OR vaccination OR immunisation OR immunization OR inoculation 1 and 2 and 3 and 4
Dates searches performed:	01 May 2018

Exclusion / Inclusion Criteria
Exclusion:	Non English language papers Single case reports Book chapters and literature reviews without novel information Not relevant to the question
Inclusion:	Papers comparing physical or clincopathological data, in sports horses exercising after revaccination for equine influenza or equine influenza and equine herpes virus 1&4 were evaluated. Due to the absence of published data in sports horses after biannual vaccination for EI, varying vaccination protocols were included.

Search Outcome
Database	Number of results	Excluded – [Non English Language]	Excluded – [single case report]	Excluded – [Narrative review/opinion pieces]	Excluded – [not relevant to PICO]	Total relevant papers
CAB Abstracts	188	37	2	5	139	5
NCBI Pubmed	25	2	0	0	22	1
Total relevant papers when duplicates removed						5

The author declares no conflicts of interest.

1. Goundasheva[sic], D., Chenchev, I., Katsarova, R., Karadiov, T., Tsachev, I., Barzey, G. (2005). "Changes in leukocyte and antibody response following exercise in horses with booster vaccination against influenza and herpes virus 4/1." Revue de Medecine Veterinaire 156(11): 527–532.
2. (A) Gundasheva, D. (2015). "Effect of exercise on erythron, heart and respiratory rates in horses vaccinated against equine herpes virus 4/1 and equine influenza virus." Comparative Clinical Pathology 24(6): 1565–1572. DOI: http://dx.doi.org/10.1007/s00580-015-2117-9
3. (B) Gundasheva, D. (2015). "Electrophoretic Analysis of Serum Proteins in Strenuously Trained Horses Revaccinated Against Equine Herpes Virus 4/1 and Equine Influenza Virus." Veterinarija ir Zootechnika 69(91): 18–25.
4. Gundasheva, D., & Georgieva, T. (2015). "Changes in some acute phase response parameters after physical exercise in horses with booster vaccination against equine herpes virus 4/1 and equine influenza virus." Veterinarija ir Zootechnika 70(92): 22–28.
5. Sotirov, L., Goundasheva, D., Dzheleboy, P. (2004). "Lysozyme and complement response to exercise in horses with booster vaccination against influenza virus and equine herpes virus 1 and 4." Revue de Medecine Veterinaire 155(8/9): 449–452.

RCVS Knowledge was supported in producing this Knowledge Summary by an educational grant from Petplan Charitable Trust.