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The newly emerging, highly pathogenic avian influenza (HPAI) H5N8 virus of clade 2.3.4.4 was recently detected in wild birds and domestic poultry in Egypt in the 2016/2017 winter season. Vaccination based on commercial H5 vaccines is used as an essential control strategy in Egyptian poultry. Here, we studied the efficacy of the eight most common commercial H5 poultry vaccines in the Egyptian market and compared them with an experimental vaccine based on the Egyptian LPAI H5N8 virus that was prepared by using reverse genetics. The experimental vaccine and Re-5 commercial vaccine were able to completely protect chickens and significantly reduce virus shedding. Our results indicate that most of the commercial poultry H5 vaccines used in the present study were ineffective because the seed viruses in these vaccines are genetically distinct from the H5N8 viruses currently circulating in Egypt. Although some of the commercial vaccines protected chickens from mortality, they failed to prevent chickens from shedding the virus. Accordingly, we recommend updating and reinforcing the H5N8 prevention and control strategies in Egypt. The vaccination strategy should be reconsidered based on currently circulating viruses.

Highly pathogenic avian influenza viruses are circulating in lots of avian species, causing major outbreaks in both wild and domestic poultry. Since its first emergence in 2014, clade 2.3.4.4 H5N8 viruses widely spread in the world resulting in enormous economic losses. In Egypt, the newly emerging high pathogenic avian influenza (HPAI) H5N8 viruses have been detected in domestic poultry and in wild birds since the 2016/2017 winter season. AI H5N8 is cocirculating with LP H9N2 and HP H5N1 in the Egyptian environment. Poultry vaccination strategy in Egypt is based on commercially available H5 vaccines as an essential control policy, while the majority of commercial avian influenza H5 vaccines utilized in Egypt are not effective against H5N8 viruses. The present study included 3 experimental H5N8 inactivated vaccines based on the 2 major antigenic proteins of the currently circulating strain A/chicken/Egypt/Q16684C/2019 (H5N8), and the internal segments of the A/PR/8/1934 (H1N1) virus. Then, the protective efficacy of the three forms of inactivated vaccines (HAH5N8+7PR8, NAH5N8+7PR8 and HA, NAH5N8+6PR8) were compared regarding the parental PR8 virus in vaccinated specific pathogen free chickens. The NAH5N8+6PR8 as well as HAH5N8+7PR8 and HA vaccines showed the highest protection capacity of challenged SPF chickens and were able to elicit the highest titers of virus-neutralizing antibodies. Thus, a continuous active surveillance strategy is needed to determine the most dominant circulating strain and updating of vaccine seed strains. [ABSTRACT FROM AUTHOR]

Since its emergence in 2014, the highly pathogenic avian influenza H5N8 virus has continuously and rapidly spread worldwide in the poultry sector resulting in huge economic losses. A typical inactivated H5N8 vaccine is prepared using the six internal genes from A/PR8/1934 (H1N1) and the two major antigenic proteins (HA and NA) from the circulating H5N8 strain with the HA modified to a low pathogenic form (PR8HA/NA-H5N8). The contribution of the other internal proteins from H5N8, either individually or in combination, to the overall protective efficacy of PR8-based H5N8 vaccine has not been investigated. Using reverse genetics, a set of PR8-based vaccines expressing the individual proteins from an H5N8 strain were rescued and compared to the parent PR8 and low pathogenic H5N8 strains and the commonly used PR8HA/NA-H5N8. Except for the PR8-based vaccine strains expressing the HA of H5N8, none of the rescued combinations could efficiently elicit virus-neutralizing antibodies. Compared to PR8, the non-HA viral proteins provided some protection to infected chickens six days post infection. We assume that this late protection was related to cell-based immunity rather than antibody-mediated immunity. This may explain the slight advantage of using full low pathogenic H5N8 instead of PR8HA/NA-H5N8 to improve protection by both the innate and the humoral arms of the immune system. [ABSTRACT FROM AUTHOR]