Submitted to: Vaccine
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/12/2011
Publication Date: 10/1/2011
Citation: Abbas, M.A., Spackman,E., Fouchier, R., Smith, D., Ahmed,Z., Siddique,N., Sarmento,L., Naeem,K., McKinley, E.T., Hameed,A., Rehmani,S., Swayne, D.E. 2011. H7 avian influenza virus vaccines protect chickens against challenge with antigenically diverse isolates. Vaccine. 29(43):7424-7429. Interpretive Summary: Vaccination is a crucial method for the control of bird flu, however the virus is able to mutate very quickly so vaccines may not protect against new strains as they emerge. In this study we characterized the strains of a type of bird flu viruses which are endemic in much of the world, known as H7. Pakistan has had sporadic outbreaks of H7 bird flu, which they have controlled through vaccination, therefore viruses from several outbreaks in Pakistan were used to determine if vaccines made from virus collected in the 1990’s would still work. Also, newer viruses were assessed for their ability to protect chickens against the newer strains of H7. The genetics of these viruses and components that are recognized by the immune system were also compared among the viruses from Pakistan and with H7 bird flu from the Americas and Europe. It was found that newer strains did protect better and that over the years the H7 bird flu viruses in Pakistan have undergone some mutation.
Technical Abstract: Vaccination has been a critical tool in the control of some avian influenza viruses (AIV) and has been used routinely in Pakistan to help control sporadic outbreaks of highly pathogenic (HP) H7 AIV since 1995. During that time, several AIV isolates were utilized as inactivated vaccines with varying degrees of success. In order to evaluate which H7 AIV strains may serve as optimal vaccines for diverse H7 AIVs from Pakistan we conducted vaccination-challenge studies with five H7 vaccines against challenge with two HPAIVs: A/chicken/Murree/NARC-1/1995 H7N3 and A/chicken/Karachi/SPVC-4/2004 H7N3. To further characterize the isolates antigenic cartography was used to visually demonstrate the antigenic relationships among the isolates. All vaccines provided similar protection against mortality, morbidity and shedding of challenge virus from respiratory tract. However, some minor (not significant) differences were observed and correlated with antibody levels induced by the vaccine prior to challenge.