The leading candidate appears to be the Zoetis vaccine targeting H5N2 — even though the dominant strain spreading through U.S. flocks is H5N1 clade 2.3.4.4b.
The vaccine uses the N2 neuraminidase subtype deliberately to support DIVA (Differentiating Infected from Vaccinated Animals) surveillance — allowing authorities to detect field infections in vaccinated birds.
In February 2025, the USDA issued a conditional license to Zoetis for its Avian Influenza Vaccine, H5N2 Subtype, Killed Virus, specifically for use in chickens, based on a “reasonable expectation of efficacy based on serology data”. In other words, the approval rests on hope that antibody titers will translate into real-world protection—not on demonstrated effectiveness against infection or transmission.
A conditional license allows the vaccine to be used immediately, but only under specific circumstances—such as during an outbreak or in targeted populations. As of June 2025, Zoetis’s H5N2 vaccine remains the only avian influenza vaccine conditionally approved by the USDA for use in U.S. poultry. No other vaccines are currently authorized or ready for large-scale deployment.
However, according to the USDA, inactivated virus vaccines—such as the Zoetis H5N2 formulation—are non-sterilizing in the field. This means they do not prevent infection, do not eliminate viral shedding, and allow vaccinated birds to silently carry and transmit H5N1, particularly in densely populated commercial flocks.
Hellbound and Down 