Combined H5ND inactivated vaccine protects chickens against challenge by different clades of highly pathogenic avian influenza viruses subtype H5 and virulent Newcastle disease virus.

AIM: The aim of the current study was to evaluate the efficacy of a trivalent-inactivated oil-emulsion vaccine against challenge by different clades highly pathogenic avian influenza (HPAI) viruses including HPAI-H5N8 and the virulent genotype VII Newcastle disease virus (NDV) (vNDV). MATERIALS AND METHODS: The vaccine studied herein is composed of reassortant AI viruses rgA/Chicken/Egypt/ME1010/2016 (clade 2.2.1.1), H5N1 rgA/Chicken/Egypt/RG-173CAL/2017 (clade 2.2.1.2), and "NDV" (LaSota NDV/CK/Egypt/11478AF/11); all used at a concentration of 108 EID50/bird and mixed with Montanide-ISA70 oil adjuvant. Two-week-old specific pathogen free (SPF) chickens were immunized subcutaneously with 0.5 ml of the vaccine, and hemagglutination inhibition (HI) antibody titers were monitored weekly. The intranasal challenge was conducted 4 weeks post-vaccination (PV) using 106 EID50/0.1 ml of the different virulent HPAI-H5N1 viruses representing clades 2.2.1, 2.2.1.1, 2.2.1.2, 2.3.4.4b-H5N8, and the vNDV. RESULTS: The vaccine induced HI antibody titers of >6log2 against both H5N1 and NDV viruses at 2 weeks PV. Clinical protection against all HPAI H5N1 viruses and vNDV was 100%, except for HPAI H5N1 clade-2.2.1 and HPAI H5N8 clade-2.3.4.4b viruses that showed 93.3% protection. Challenged SPF chickens showed significant decreases in the virus shedding titers up to <3log10 compared to challenge control chickens. No virus shedding was detected 6 "days post-challenge" in all vaccinated challenged groups. CONCLUSION: Our results indicate that the trivalent H5ND vaccine provides significant clinical protection against different clades of the HPAI viruses including the newly emerging H5N8 HPAI virus. Availability of such potent multivalent oil-emulsion vaccine offers an effective tool against HPAI control in endemic countries and promises simpler vaccination programs.

Comparative Effectiveness of Two Oil Adjuvant-Inactivated Avian Influenza H9N2 Vaccines.

Low pathogenic avian influenza H9N2 virus infection has been an important risk to the Egyptian poultry industry since 2011. Economic losses have occurred from early infection and co-infection with other pathogens. Therefore, H9N2 vaccination of broiler chicks as young as 7 days old was recommended. The current inactivated H9N2 vaccines (0.5 ml/bird) administered at a reduced dose (0.25 ml/bird) do not guarantee the delivery of an effective dose for broilers. In this study, the efficacy of the reduced-dose volume (0.3 ml/bird), compared with the regular vaccine dose (0.5 ml/bird) of inactivated H9N2 vaccines using two different commercially available adjuvants, was investigated. The vaccines were prepared from the local H9N2 virus (Ck/EG/114940v/NLQP/11) using the same antigen content: 300 hemagglutinating units. Postvaccination (PV) immune response was monitored using the hemagglutination inhibition test. At 4 wk PV, both vaccinated groups were challenged using the homologous H9N2 strain at a 50% egg infective dose (EID50) of 10(6) EID50/bird via the intranasal route. Clinical signs, mortality, and virus shedding in oropharyngeal swabs were monitored at 2, 4, 6, and 10 days postchallenge (DPC). The reduced-dose volume of vaccine induced a significantly faster and higher immune response than the regular volume of vaccine at 2 and 3 wk PV. No significant difference in virus shedding between the two vaccine formulas was found (P ≥ 0.05), and both vaccines were able to stop virus shedding by 6 DPC. The reduced-dose volume of vaccine using a suitable oil adjuvant and proper antigen content can be used effectively for early immunization of broiler chicks.

A Dose-Response Study of Inactivated Low Pathogenic Avian Influenza H9N2 Virus in Specific-Pathogen-Free and Commercial Broiler Chickens.

Since the first report of low pathogenic avian influenza (LPAI) H9N2 virus in Egypt in 2011, the Egyptian poultry industry has suffered from unexpected economic losses as a result of the wide spread of LPAI H9N2. Hence, inactivated H9N2 vaccines have been included in the vaccination programs of different poultry production sectors. The optimal antigen content of avian influenza virus vaccines is essential to reach protective antibody titers. In this study, the correlation between antigen content (based on hemagglutinating units [HAU]) and postvaccination (PV) antibody response of H9N2 inactivated vaccine was studied. Five different vaccine antigen loads (128, 200, 250, 300, and 350 HAU formulas/dose) were investigated in commercial broiler and specific-pathogen-free (SPF) chickens. Vaccine safety and PV antibody responses were monitored. At the fourth week PV only SPF vaccinated groups (128, 200, 250, and 300 HAU/dose) were challenged using LPAI H9N2 (A/Ck/EG/114940v/NLQP/11) virus with 10(6) EID50/bird. Oropharyngeal swabs were used to monitor virus shedding at 2, 4, 6, and 10 days postchallenge. Results showed that all vaccine formulations were well tolerated, and the highest antibody titers were observed in birds vaccinated with higher HAU. Vaccines containing 128 and 200 HAU/dose did not induce the required protective HI titers by 3 wk PV. Meanwhile, the challenge experiment in SPF chickens showed that 250 and 300 HAU vaccine doses were required to reduce the level and duration of virus shedding. Study results thus suggest that inactivated H9N2 vaccines containing at least 250 HAU/dose will induce the optimal protective titers and minimize virus shedding in SPF chickens.