Techniques to increase the yield in manufacturing avian influenza vaccines may help improve the response to a pandemic, in which widespread and rapid vaccination offers the best hope of controlling infection.
Chinese scientists have reported good results from an inactivated adjuvanted whole-virion vaccine against the H5N1 strain of the influenza A virus. A clinical trial in 120 volunteers tested four different strengths of the vaccine, with two doses given four weeks apart. All four formulations elicited an antibody response after the first dose. The highest immune response, with 78% of patients becoming seropositive, was seen with the highest strength containing 10 micrograms of haemagglutinin. There were no serious adverse events and most local and systemic reactions were mild and transient.
Other avian influenza vaccines had been developed using a split-virion technique which was less immunogenic and thought to be better tolerated. "Although whole-virion influenza vaccines are generally thought to be more reactogenic, our results indicate that the frequencies of local and systemic events with the two-dose regimen used here are low and comparable with split-virion vaccines," the reserachers said. One possible explanation was that the whole-virion vaccines had a lower total antigen content.
During a pandemic, the demand for influenza vaccines will far outstrip the manufacturing capacity, a situation that has led to WHO encouraging investigation into dose-sparing strategies, including the use of adjuvants and whole-virion vaccine," they said. Up to 30% of antigen could be lost during preparation of split-virion products.
By August 2006 there had been 241 human cases of avian influenza reported to WHO, of whom 141 had died. Despite limited evidence of person-to-person transmission, the threat of a pandemic remained very real.
Reference
Lin, J. Zhang, J. et al. 2006, 'Safety and immunogenicity of an inactivated adjuvanted whole-virion influenza A (H5N1) vassine: a phase I randomised controlled trial', Lancet, vol. 368, pp. 991-997.
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