Efficacy of rHVT-AI Vector Vaccine in Broilers with Passive Immunity Against Challenge with Two Antigenically Divergent Egyptian Clade 2.2.1 HPAI H5N1 Strains

Abstract

In countries where avian influenza has become endemic, early vaccination of layer pullets or broilers with classical inactivated vaccines at the hatchery is no longer an option because of interference with passive immunity indirectly induced by the necessary vaccination of the breeders. On the other hand, injection of thousands of chicks from 7 to 10 days old on farms has been determined to be unreliable and, therefore, poorly efficacious. For these reasons, interest has arisen regarding a newly developed live recombinant vector vaccine based on a turkey herpesvirus (HVT) expressing the H5 gene from a clade 2.2 H5N1 highly pathogenic avian influenza virus (HPAIV) strain (rHVT-H5), which in theory is capable of breakthrough passive immunity to both the vector (HVT) and the insert (H5) and is consequently applicable at the hatchery. The objectives of this trial were to evaluate the impact of maternally derived antibodies (MDAs) specific to H5N1 on the immunity and the efficacy (protection and virus shedding) of different vaccination programs including rHVT-H5 and inactivated H5N1 and H5N2 vaccines applied alone or in combination. Therefore, broilers carrying MDAs against both HVT and Asian H5N1 HPAIV were vaccinated on the first day of age with rHVT-H5, with or without boosting vaccination by an inactivated vaccine after 10 days. The different groups were challenged with two antigenically highly divergent Egyptian dade 2.2.1 H5N1 HPAIVs at 4 wk of age. Protection against challenge was compared with unvaccinated birds or vaccinated birds without MDAs. Between 70% and 90% clinical protection could be observed in the vaccinated groups possessing MDAs, indicating no or very low interference of MDAs with vaccination. Results regarding clinical protection, humoral, cell-mediated, and mucosal immunity, as well as re-excretion of challenge virus are presented and discussed.

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

“…This prime/boost vaccination regime has also induced the highest humoral immunity against both antigens (C/H5N1/Ag and V/H5N1/Ag). Similar results in broiler chickens were also previously reported by Rauw, et al (2012). When MDA interference is compared, looking at the post-vaccination immune response, the highest MDA interference occurred in Group II vaccinated with KV-H5 vaccine and the lowest impact of MDA interference occurred in Group III vaccinated with the prime/boost.…”

“…Hatchery vaccination administered at day old, if effective, would optimize vaccine coverage and flock protection levels with the use of limited resources (Peyre, 2014). One of the main limitations of inactivated vaccines is that they mainly induce humoral immune response (Bermudez & Stewart-Brown, 2003;Lambrecht et al, 2004;Marangon & Busani, 2006;Rauw, et al, 2012), and face high levels of interference with MDAs when administered within the first 10 days of age (De Vriese et al, 2010;Maas et al, 2011;Abdelwhab, et al, 2012b), as per current practice in Egypt. The rHVT-H5 vaccine, expressing the HA gene of a HPAI H5N1 clade 2.2 A/Swan/Hungary/499/2006 strain inserted into the FC-126 strain of the HVT vector, has been developed to fight current AI threats to the poultry industry (Rauw, et al 2011).…”

“…When MDA interference is compared, looking at the post-vaccination immune response, the highest MDA interference occurred in Group II vaccinated with KV-H5 vaccine and the lowest impact of MDA interference occurred in Group III vaccinated with the prime/boost. Rauw, et al (2012) showed that rHVT-H5/inactivated H5N2 (prime/boost) vaccination regime induces a higher level of humoral and mucosal IgG and IgM as well as stronger cell-mediated immunity as compared to vaccinations with rHVT-H5 alone or with inactivated H5N2 vaccine alone.…”

Comparison of single 1-day-old chick vaccination using a Newcastle disease virus vector with a prime/boost vaccination scheme against a highly pathogenic avian influenza H5N1 challenge

“…In order to complete the characterization of H5 humoral response, the challenge strain (H5N1) and a reference strain (H5N3; Laboratory of European Union, VLA, Weybridge, UK) were used to perform the HI tests because of their high antigenic similarity. This approach, presenting two complementary tests, has previously been reported to characterize the H5 humoral response after vaccination and challenge experiments (Rauw et al, , 2012.…”

Effect of biosecurity measures and early detection systems, mitigation measures and surveillance strategies on the spread of HPAI and LPAI between farms

“…The European Food Safety Authority reserves its rights, view and position as regards the issues addressed and the conclusions reached in the present document, without prejudice to the rights of the authors. (Rabl et al, 2009) Language (Ramakrishnan et al, 2009) Not relevant outcomes (Ramey et al, 2014) Not relevant outcomes (Ramis et al, 2014) Not relevant outcomes (Rauw et al, 2012) Not relevant outcomes (Rauw et al, 2011) Not relevant outcomes (Rawdon et al, 2010 (Sakoda et al, 2012) Territory (Saksena et al, 2015) Territory (Salman, 2009) Not relevant outcomes (Sansyzbay et al, 2013) Study population (Sarikaya and Erbaydar, 2007) Study population (Sartore et al, 2010) Not relevant outcomes (Schmitz et al, 2013) Not relevant outcomes (Schroeer et al, 2009) Not relevant outcomes (Schroeer et al, 2011) Not relevant outcomes (Schultsz et al, 2009) Study population (Schweiger and Buda, 2013) Language Study population (Senne, 2010) Territory The present document has been produced and adopted by the bodies identified above as authors. This task has been carried out exclusively by the authors in the context of a contract between the European Food Safety Authority and the authors, awarded following a tender procedure.…”