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Biosecurity BriefingStudy Shows Positive Clinical Results for Whole Virus H5N1 Vaccine Grown in Cell Culture By Jennifer Nuzzo, June 20, 2008 On June 12, 2008, the New England Journal of Medicine published results from a randomized clinical trial of a whole virus H5N1 avian influenza vaccine that was produced in cell-culture. The authors report that two doses of unadjuvanted vaccine produced evidence of a positive immune response for three clades of the H5N1 virus, with side-effects comparable to both split-antigen H5N1 vaccines and other whole-virus H5N1 vaccines with adjuvant that are grown in eggs.1 The authors conducted the “randomized, dose-escalation phase 1 and 2” study at three sites in Austria (n=1) and Singapore (n=2).1 Between June and September 2006, 275 healthy male and female patients (ages 18 to 45) received one of six possible vaccine formulations: 3.75 µg of antigen with adjuvant (n=45 patients); 7.5 µg with adjuvant (n=45); 7.5 µg without adjuvant (n=45); 15 µg with adjuvant (n=46); 15 µg without adjuvant (n=45); 30 µg with adjuvant (n=49). The vaccine was based on the clade 1 H5N1 virus (A/Vietnam/1203/2004). Patients in each study group received a second dose of vaccine 21 days after their first dose. There was no placebo group. The investigators report that the highest antibody response was noted in the group that received the vaccine with 7.5 µg of antigen and no adjuvant. The authors estimated seroconversion to be 69% among patients in that study group. Adjuvants “did not improve the antibody response.” Among all patients receiving vaccine, reports of side effects were generally mild (mild pain at injection site and headache were most common) and comparable to those reported for other H5N1 vaccines (including subvirion vaccines and whole virus vaccines grown in eggs). The authors also found that the “whole-virus clade 1-based vaccine” induced “a substantial…response against clade 2 and clade 3 strains” of the H5N1 virus.1 The study notes that the development of whole virus vaccines may offer advantages in a pandemic setting, as there is some evidence that they produce a positive immune response at smaller doses than vaccines that are created from only the surface antigens of the influenza virus. Moreover, vaccines that are grown in cell culture provide a “robust manufacturing platform that eliminates dependence on embryonated chicken eggs, which would be an advantage in the event of limited availability of such eggs during a pandemic caused by a highly pathogenic avian virus.”1 Baxter Bioscience developed the study vaccine.1 As reported in a previous Biosecurity Briefing, the Republic of Indonesia, which signed a memorandum of understanding with Baxter last year, recently accused the drug manufacturer of “moving too slowly in developing a bird flu vaccine using the [country’s] virus strain.”2 References
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