Serological baseline, antibody stability and efficacy of different types of avian influenza (H5) vaccines.

Abstract

Importance: Evaluating Iran's national highly pathogenic avian influenza (HPAI) control program can inform vaccine selection, optimize immunization duration, guide exit strategies, and assess hemagglutination inhibition (HI) and serum neutralization (SN) methods.

Objective: To establish a serological baseline, assess antibody stability, and compare the efficacy of three HPAI (H5) vaccines.

Methods: We analyzed over 9,000 blood samples and 6,420 swabs from approximately 1.5 million birds up to 64 weeks old. HI (β, α), RT-PCR, and SN tests were conducted, with statistical analysis performed using two-way ANOVA.

Results: The serological baseline (GM titer) using H5N8 antigens from A/Chicken/Iran/162/2016 varied. The Re6+Re8 vaccine produced higher and more stable HI β titers than the H5N3 and baculovirus vaccines. Serum HI α neutralization ability was similar for Re6+Re8 and H5N3 vaccines, both 100 times greater than the baculovirus vaccine. Neutralization indices for H5N3, Re6+Re8, and baculovirus vaccines were 4.7, 4.5, and 4.2 (log2), respectively.

Conclusions and relevance: After two vaccinations, Re6+Re8 exhibited the most stable HI β antibody response, while H5N3 had the highest neutralization index, surpassing Re6+Re8 by 0.2 and the baculovirus vaccine by 0.5. These findings highlight discrepancies between HI β and SN test results, with SN being a stronger indicator of protective titers due to its in vivo methodology, compared to the in vitro HI assay.