|
| ||||||||
| ||||||||
|
Biosecurity News in Brief
Research Suggests that Prior Immunity to Seasonal Influenza May Provide Partial Protection against Avian H5N1 InfluenzaBy David Press and Jennifer Nuzzo, February 16, 2007 In the February 2007 edition of the Public Library of Science (PLoS) Medicine journal, a study[1] by a research team led by Richard Webby of St. Jude’s Children’s Research Hospital investigated whether immunity to the human seasonal influenza strain, H1N1, may confer immunity to the avian influenza virus, H5N1. The found that mice immunized against the neuraminidase antigen of a human seasonal influenza virus, H1N1, were partially protected against subsequent infection with the H5N1 avian influenza virus. In addition, a limited serological survey suggests that some people who carry antibodies that react to the N1 in the avian H5N1 virus. In light of these results, the researchers suggest that immunization with the seasonal influenza vaccine, which contains the H1N1 strain, may provide some immunity against the H5N1 avian influenza strain. The researchers completed this investigation in three parts. In the first part, the researchers analyzed whether mice vaccinated with DNA encoding for the neuraminidase antigen N1 (huN1) from a human H1N1 influenza virus, would survive when inoculated with supra-lethal doses one of the following viruses: 1) a genetically-manipulated virus bearing an N1 neuraminidase derived from a human influenza virus (Pr8-huN1); 2) a genetically-manipulated virus bearing an N1 neuraminidase derived from an avian influenza virus (Pr8-avN1); or 3) an avian H5N1 influenza virus which was isolated from a human patient in Vietnam. In each challenge group, mice were given either a high or a lose dose of virus (100 or 10 times the mouse-lethal dose of H5N1, respectively). One hundred percent of mice vaccinated with huN1 survived inoculation with the human N1 bearing virus at all doses. Fifty-percent of mice inoculated with lower doses of either H5N1 or the avian N1-bearing virus at high and low doses survived; those that received the highest challenge dose did not survive. By comparison, all of the control mice in each viral challenge group that did not receive a vaccine against huN1 died.[1] In the second part of the investigation, they tested whether antibodies raised against huH1 after vaccination were responsible for the survival of half of the mice infected with H5N1, by injected serum from the mice that survived infection with H5N1 into a second group of unvaccinated mice. This second group of mice was then infected with H5N1. Similar to results from the prior experiment, 46% (6/13) of the mice that had been injected with the serum from first group survived H5N1 infection.[1] Lastly, Webby’s team tested human serum from 38 volunteers to look for antibodies that may inhibit the H5N1 virus. Eighty-two percent (31/38) of the human samples possessed antibodies that neutralized H1N1 and 18% (7/38) possessed antibodies that had low level activity against H5N1.[1] In light of these results, the researchers concluded that “immunization against H1N1 influenza virus… containing [neuraminidase] protein or via natural H1N1 infection can provide humans with some degree of resistance to H5N1 influenza viruses.”[1] In addition, they argue that seasonal influenza vaccination may provide a “possible benefit” and “urges that emphasis be placed” on implementing its use in areas endemic to H5N1.[1] In a commentary accompanying the article,[2] Laura Gillim-Ross and Kanta Subbarao of the U.S. National Institute of Allergy and Infectious Diseases caution that while the results of the study are “very intriguing”, they are “insufficient to conclude” that seasonal influenza vaccination will provide immunity in some individuals against H5N1. Consequently, they contend widespread application of these findings would be “premature”.[2] Among Gilliam-Ross and Subbarao’s concerns, they caution that Webby and his colleagues have not yet established the “level of antibodies necessary” to afford such protection against H5N1, which “strain of avian influenza” will ultimately lead to an epidemic, or if one dose of current seasonal vaccination will be enough to prevent illness due to different immunogenicity between different viral strains.[2]
|