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The global spread of highly pathogenic avian influenza (HPAI) A (H5N1) clade 2.3.4.4b virus since 2021 necessitates a re-evaluation of the role of vaccination in controlling HPAI outbreaks among poultry, which has been controversial because of the concern of silent spread with spillover to wild birds and human. To inform policymaking, we systematically reviewed and meta-analyzed all existing data from experimental challenge trials to assess the efficacy of HPAI vaccines against mortality in specific pathogen free (SPF) chickens, with evaluation of the certainty of evidence (CoE) using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach. Out of 223 screened publications, 46 trials met our eligibility criteria. Inactivated vaccines showed an efficacy of 95% (risk ratio RR = 5% 95% CI: 1% to 17%, I2 = 0%, CoE high) against homologous strains and an efficacy of 78% (RR = 22% 95% CI: 14% to 37%, I2 = 18%, CoE high) against heterologous strains (test for subgroup difference P = 0.02). Live recombinant vaccines exhibited the highest efficacy at 97% (RR = 3% 95% CI: 1% to 13%, I2 = 0%, CoE high). Inactivated recombinant vaccines had an overall efficacy of 90% (RR = 10% 95% CI: 6% to 16%, I2 = 47%, CoE high). Additionally, current commercial vaccines showed an overall efficacy of 91% (RR = 9% 95% CI: 5% to 17%, I2 = 23%, CoE high), with 96% efficacy (RR = 4% 95% CI: 1% to 21%, I2 = 0%, CoE high) against homologous strains and 90% efficacy (RR = 10% 95% CI: 5% to 20%, I2 = 31%, CoE moderate) against heterologous strains. Our results show that vaccination, which does not completely mask HPAI-related mortality among poultry, needs to be a part of a comprehensive new global avian influenza control strategy.
Tseng et al. (Thu,) studied this question.