Main points from the AAAP Fact Sheet on H5N1 vaccination
The AAAP Board of Directors have approved of a fact sheet on H5N1, created by a group of AAAP experts consisting of Dr. Suzanne McComb, Dr. David Swayne, Dr. David Suarez, and Dr. Erica Spackman.
Severity of the H5N1 2.3.4.4b Outbreak:
- This clade has caused an unprecedented global panzootic in poultry, wild birds, and mammals.
- Traditional control methods (biosecurity, surveillance, stamping-out) are no longer sufficient due to endemic circulation in wild birds and high susceptibility of poultry.
Role of Vaccination:
- Matched vaccines can enhance resistance to infection and reduce virus shedding, breaking transmission cycles.
- Proper application (correct strain, route, age, dosage) is critical.
Limitations of Vaccination:
- Vaccination cannot replace biosecurity or stamping-out of infected flocks.
- Mismatched vaccines may worsen outbreaks by encouraging escape variants.
- Vaccination crews must strictly observe biosecurity.
Available Vaccines in the U.S.:
- Five USDA-licensed H5 vaccines exist; four (inactivated, RNA, two rHVT-H5) have shown efficacy against 2.3.4.4b.
- Single doses are insufficient; booster doses are needed for sustained protection.
Regulatory Status:
-Poultry vaccination is not currently approved in the U.S. due to trade concerns.
- Vaccines have been used in endangered species (e.g., California condor).
- Regulatory approval by both USDA and individual states is required.
Logistics and Target Use:
- Vaccines can be integrated into current poultry vaccination programs (e.g., in ovo, day-old chicks).
- Targeted use recommended in high-risk poultry (e.g., layers, turkeys) and defined geographic zones.
- Broiler exports should be minimally impacted.
Silent Infections:
- Rare when well-matched vaccines are properly used in well-managed flocks (e.g., France, Hong Kong experience).
Vaccine Bank:
- The U.S. no longer maintains a national H5 vaccine bank, but some vaccines (e.g., rHVT-H5) are commercially available.
Monitoring Vaccinated Flocks:
- Immune monitoring (HI, ELISA, PCR) is essential to confirm flock-level protection.
- Antibody titers and vaccine virus replication (e.g., in rHVT-H5) can be used for assessment.
Surveillance in Vaccinated Flocks (DIVA approach):
- Must focus on detecting virus, especially via virological methods (rRT-PCR).
- Sampling should target mortality and sick birds; environmental swabs may offer cost-effective early detection.
- Serological surveillance is complex and depends on vaccine type (e.g., H5-only vs. whole virus).
