The potential impact of a single amino-acid substitution on the efficacy of equine influenza vaccines.
Authors: Yamanaka T, Cullinane A, Gildea S, Bannai H, Nemoto M, Tsujimura K, Kondo T, Matsumura T
Journal: Equine veterinary journal
Summary
# Editorial Summary: Equine Influenza Vaccine Efficacy and Amino-Acid Variation Antigenic drift in equine influenza viruses poses a significant challenge to vaccine effectiveness, particularly when circulating field strains diverge from vaccine components. This Japanese team investigated how a single amino-acid substitution in the haemagglutinin protein of Florida clade 2 (Fc2) influenza viruses might compromise protection offered by vaccines containing only Florida clade 1 (Fc1) strains—a situation that had persisted in Japanese vaccination programmes despite OIE recommendations for inclusion of both clades. Using serological and viral challenge data, the researchers demonstrated that even minor antigenic variations between vaccine and field strains can substantially reduce neutralising antibody responses and protective efficacy. Their findings underscore why regular vaccine strain updates are critical: reliance on outdated vaccine formulations leaves vaccinated horses vulnerable to emerging field variants, particularly when divergent clades are circulating. For practitioners in regions where Fc2 strains are prevalent, these results highlight the importance of confirming that stud and competition horses receive vaccines matched to locally circulating viruses, and support the case for advocating vaccine policy updates with national regulatory bodies when epidemiological evidence warrants it.
Read the full abstract on PubMed
Practical Takeaways
- •Ensure vaccination protocols include both Fc1 and Fc2 sublineage viruses as recommended by OIE to maintain optimal protection against current circulating strains
- •Monitor for potential vaccine efficacy gaps in regions using older vaccine formulations that lack recommended viral sublineages
- •Be aware that minor genetic changes in influenza viruses can reduce vaccine effectiveness, necessitating periodic vaccine updates
Key Findings
- •Single amino-acid substitutions in vaccine strains can significantly impact antigenic relatedness to challenge viruses
- •Japanese equine influenza vaccines have not been updated to include Florida clade 2 (Fc2) viruses despite OIE recommendations for both Fc1 and Fc2 inclusion
- •Vaccine efficacy is dependent on antigenic relatedness between vaccine strain and circulating challenge virus