A single vaccination of commercial broilers does not reduce transmission of H5N1 highly pathogenic avian influenza

Abstract

Vaccination of chickens has become routine practice in Asian countries in which H5N1 highly pathogenic avian influenza (HPAI) is endemically present. This mainly applies to layer and breeder flocks, but broilers are usually left unvaccinated. Here we investigate whether vaccination is able to reduce HPAI H5N1 virus transmission among broiler chickens. Four sets of experiments were carried out, each consisting of 22 replicate trials containing a pair of birds. Experiments 1-3 were carried out with four-week-old birds that were unvaccinated, and vaccinated at day 1 or at day 10 of age. Experiment 4 was carried out with unvaccinated day-old broiler chicks. One chicken in each trial was inoculated with H5N1 HPAI virus. One chicken in each trial was inoculated with virus. The course of the infection chain was monitored by serological analysis, and by virus isolation performed on tracheal and cloacal swabs. The analyses were based on a stochastic SEIR model using a Bayesian inferential framework. When inoculation was carried out at the 28th day of life, transmission was efficient in unvaccinated birds, and in birds vaccinated at first or tenth day of life. In these experiments estimates of the latent period (~1.0 day), infectious period (~3.3 days), and transmission rate parameter (~1.4 per day) were similar, as were estimates of the reproduction number (~4) and generation interval (~1.4 day). Transmission was significantly less efficient in unvaccinated chickens when inoculation was carried out on the first day of life. These results show that vaccination of broiler chickens does not reduce transmission, and suggest that this may be due to the interference of maternal immunity.

Comparison of the effectiveness of rHVT-H5, inactivated H5 and rHVT-H5 with inactivated H5 prime/boost vaccination regimes in commercial broiler chickens carrying MDAs against HPAI H5N1 clade 2.2.1 virus

“…Differences in MDA's half-life between the vaccinated and unvaccinated groups may suggest a possible interference of MDAs with the induction of the humoral response by AI vaccines. Indeed, MDA's such interference with the development of an immune response against various antigens has been recorded after the application of inactivated vaccines (Poetri et al, 2011). On the other hand, MDA against HVT is present in commercial DOCs.…”

Vaccination with Recombinant RNA Replicon Particles Protects Chickens from H5N1 Highly Pathogenic Avian Influenza Virus

“…This goal may be achieved using inactivated influenza virus vaccines [16], [17], [50]. However, there are also examples showing that inactivated vaccines sometimes fail to prevent virus shedding, especially if birds were immunized only once, or if the vaccine strain did not adequately match the HA antigen of the challenge virus [14], [51]. Interestingly, vaccination of chickens with recombinant VRPs expressing HA H5-HP (clade 2.5) abolished cloacal and oropharyngeal shedding of A/whooper swan/Mongolia/3/2005 (clade 2.2).…”

“…These vaccines have the advantage of being safe, but they also come with a number of shortcomings. For example, inactivated vaccines have to be repeatedly applied to induce full-protective and long-lasting immune responses in poultry [14]. Because inactivated influenza virus vaccines do not provide danger signals that would sufficiently trigger innate immunity, they are often formulated and applied with adjuvants [15]–[17].…”

Persistence and transmission of avian influenza A (H5N1): virus movement, risk factors and pandemic potential

“…In addition, H5N1 virus can replicate in clinically healthy vaccinated birds, while vaccine pressure can give rise to antigenic drift (Lee, Senne, and Suarez 2004;Peyre et al 2009). Vaccination of broiler chickens did not reduce HPAI H5N1transmission, and the authors pointed out that this was most likely due to interference of maternal immunity (Poetri et al 2011). A case-control study in the Red River Delta Region in Vietnam found that higher numbers of broiler flocks in the village increased the HPAI risk (Desvaux et al 2011).…”