Occurrence of infectious upper respiratory tract disease and response to vaccination in horses on six sentinel premises in northern Colorado.
Authors: Mumford E L, Traub-Dargatz J L, Carman J, Callan R J, Collins J K, Goltz K L, Romm S R, Tarr S F, Salman M D
Journal: Equine veterinary journal
Summary
# Editorial Summary: Vaccination Response and Respiratory Disease in Sentinel Horse Herds Conventional parenteral vaccines against equine influenza and herpesvirus frequently fail to generate detectable serum antibody responses in vaccinated horses, raising significant questions about protection efficacy in field conditions. Researchers monitored 173 horses across six Colorado premises, tracking serological responses to routine vaccination against H3N8 and H7N7 influenza strains and equine herpesviruses (EHV), whilst simultaneously documenting clinical cases of infectious upper respiratory tract disease (IURD). Seroconversion rates were disappointingly low: only 35.3% of horses mounted detectable antibody responses to EHV vaccination, whilst H7N7 and H3N8 achieved just 12.1% and 2.3% seroconversion respectively. When IURD outbreaks occurred within the monitored herds, they were predominantly associated with H3N8 influenza and *Streptococcus equi* infection—pathogens against which seroconversion had been minimal. These findings suggest that reliance on serological markers as indicators of vaccine success masks a genuine gap in respiratory protection, indicating that equine professionals should consider supplementary or alternative immunisation strategies (such as intranasal vaccination) and remain vigilant for clinical signs of disease despite documented vaccination status.
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Practical Takeaways
- •Do not assume vaccinated horses are protected from respiratory disease—many vaccinated horses fail to mount detectable antibody responses, particularly to H3N8 influenza
- •Monitor vaccinated horses clinically for signs of IURD regardless of vaccination status, as serological protection cannot be reliably predicted from vaccination records alone
- •Consider alternative or enhanced vaccination strategies beyond conventional parenteral products, as current approaches show inadequate field efficacy in protecting against respiratory pathogens
Key Findings
- •Only 35.3% of vaccinated horses seroconverted to EHV, 12.1% to H7N7 influenza, and 2.3% to H3N8 influenza despite parenteral vaccination
- •IURD outbreaks in study horses were associated with H3N8 influenza virus and Streptococcus equi despite conventional vaccination programs
- •Conventional vaccination against common respiratory viruses produced poor serological responses in a field setting on six Colorado premises