Background: Avian influenza (AI), caused by orthomyxoviruses, is a globally significant
disease affecting avian and non-avian species. It manifests in two variants, according
to the two biovariants of the virus differentiated as highly pathogenic avian influenza
(HPAI) and low pathogenic avian influenza (LPAI) strains, both of which compromise
animal welfare, reduce productivity, and cause substantial economic loss. The zoonotic
potential of HPAI strains, particularly the currently dominant clade 2.3.4.4b, raises
concerns about public health and epidemic risks. This review assesses the results
of current vaccine trials targeting HPAI clade 2.3.4.4b, emphasizing these studies
because most outbreak strains in domestic poultry currently belong to this dominant
clade. Methods: Multiple scientific databases comprised reports of research trials
on vaccine efficacy against HPAI clade 2.3.4.4b. The Boolean term “Clade 2.3.4.4b
AND vaccine” was entered into the following databases: PubMed, PubAg, Scopus, Cochrane
Library, and ScienceDirect. Results: The resulting papers were analyzed. Studies revealed
that antigenic similarity between vaccine and field strains enhances protective efficacy
(PE), reduces viral shedding, and improves hemagglutination inhibition titers. While
multivalent vaccines showed potential, results were inconsistent and varied depending
on strain compatibility. Single-dose vaccines may provide sufficient PE for poultry,
though ducks and geese often require multiple doses, and long-term PE is yet unknown.
It was discovered that vector vaccines can provide appropriate PE against clade 2.3.4.4.b.
Conclusions: Further analysis is needed as their effects may be short-lived, and subsequent
doses may be required. Limited research exists on the long-term efficacy of these
vaccines and their effectiveness in many avian species. Addressing these gaps is crucial
for optimizing vaccination strategies. A re-evaluation of vaccination strategies is
recommended but essential to implement adequate biosecurity measures on in poultry
farms. This review synthesizes current evidence and may assist veterinarians and authorities
in deciding whether to apply or license vaccines to reduce economic losses caused
by AI.
