Study: Prime-boost H5 vaccination strategy could help in pandemic
A dose of H5 avian influenza vaccine may set the stage for a stronger cellular immune response if a person later encounters a different strain of H5 virus, which suggests that this prime-boost strategy could be useful in fighting an H5N1 pandemic, according to a study reported Jul 20 in the Journal of Infectious Diseases.
The researchers, from several US institutions, looked at the effect of the prime-boost vaccine strategy on CD4+ and CD8+ T cell responses. They said T cells can recognize epitopes (components of antigens) shared by many different flu viruses and that T cells in mice provide protection against a wide range of influenza A viruses.
The study involved 517 healthy adults who had participated in any of nine earlier studies involving vaccination with a clade 1 H5 virus, a 2004 strain from in Vietnam. The volunteers had received two or three clade 1 vaccine doses between 1 and 6 months apart, with or without an adjuvant. A subset of participants was given a placebo.
In the new study, those who had received the clade 1 vaccine were randomly assigned to get a single dose of either 15 or 90 micrograms (mcg) of a vaccine based on an H5 clade 2 virus, a 2005 strain from Indonesia. The placebo recipients from the earlier trials received two doses (15 or 90 mcg) of the clade 2 vaccine, a month apart. The doses were given 2 to 3 years after the priming doses.
The team reported that those who had been primed with the clade 1 vaccine showed "significantly enhanced" cross-reactive T cell responses to the clade 2 vaccine 6 months after vaccination, compared with the placebo recipients. The amount of priming dose (15 or 90 mcg) had no effect on the magnitude of the T cell responses to the clade 2 vaccine, but the magnitude and duration of T cell responses were significantly lower in volunteers age 65 years and older.
The presence of adjuvant in the priming vaccine also was found to have a positive effect on T cell responses to the clade 2 vaccine, but it was weaker than the effect of age.
"H5 heterotypic priming prior to onset of an H5N1 pandemic may increase magnitude and duration of immunity against a newly drifted pandemic H5 virus," the authors said. But they cautioned that the true importance of the cross-reactive T cell responses can be determined only in phase 3 efficacy studies designed to look for correlations between those responses and actual protection against flu.
Jul 20 J Infect Dis abstract
Taiwan reports 3 H5N8 avian flu outbreaks in poultry
The World Organization for Animal Health (OIE) today reported details on three outbreaks of highly pathogenic H5N8 avian flu outbreaks in Taiwan. The outbreaks occurred in late June and early July and involved 2,874 birds. The source of the outbreaks is unknown at this time.
The first outbreak occurred on Jun 23 in the Wanhua district of Taipei City, and involved 103 native chickens found in a small farm's slaughterhouse. The second outbreak was on Jul 1 in the Xinhua district of Tanian City, and resulted in the death or culling of 2,230 geese. The final outbreak was reported on Jul 3 in Fangshan district, Kaohsiung City, and involved 541 slaughterhouse chickens.
The OIE said neighboring farms are being closely monitored, and weekly follow-up reports will be published.
Jul 22 OIE report