Detection of cold-adapted vaccine-strain influenza virus using two commercial assays.
Authors: Adam E N, Morley P S, Chmielewski K E, Carman J, Gonzales G
Journal: Equine veterinary journal
Summary
# Editorial Summary: Detection of Cold-Adapted Vaccine-Strain Influenza Virus Intranasal administration of cold-adapted live influenza vaccine in horses raises practical concerns for disease surveillance programmes, particularly when vaccinated and unvaccinated animals share facilities. This 2002 study evaluated how reliably two commercial antigen detection assays could identify vaccine-strain virus in nasal secretions from seven vaccinated horses and three unvaccinated contact animals over several days post-vaccination. The Flu OIA assay detected positive results across all ten horses during the study period, with peak detection occurring within the first three days of vaccination and sporadic positivity continuing thereafter; by contrast, the Directigen Flu A assay identified only a single positive sample. Most significantly, unvaccinated in-contact horses tested positive, confirming that vaccinated animals actively shed vaccine-strain virus capable of transmitting to naive horses. For practitioners managing vaccinated populations—particularly in competition yards, breeding facilities or training centres where mixed vaccination status is common—these findings underscore the critical importance of understanding assay sensitivity and the potential for false-positive results when interpreting influenza diagnostics following intranasal vaccination, and should inform protocols for quarantine and post-vaccination surveillance strategies.
Read the full abstract on PubMed
Practical Takeaways
- •When using modified-live intranasal influenza vaccine in horse populations, be aware that vaccinated horses will shed virus and can infect unvaccinated in-contact horses, so interpret positive antigen tests accordingly
- •Flu OIA assay is substantially more sensitive than Directigen Flu A for detecting vaccine-strain virus; choose your diagnostic test based on whether you need maximum sensitivity post-vaccination
- •Expect positive antigen detection results for several days after vaccination, particularly in the first 3 days—this reflects vaccine-strain shedding rather than necessarily indicating clinical infection
Key Findings
- •All 10 horses tested positive on Flu OIA assay during the study period, compared to only 1 horse on 1 sample using Directigen Flu A assay
- •Vaccinated and contact horses showed highest positivity rates during the first 3 days following vaccination
- •Non-vaccinated contact horses became infected with vaccine-strain virus shed by vaccinated horses, indicating transmissibility of the modified-live vaccine strain
- •Commercial antigen detection assays show markedly different sensitivity profiles when detecting cold-adapted vaccine-strain influenza virus