A subvirion inactivated H5N1 avian flu vaccine produced a weak immune response after two high-antigen doses, regardless of whether volunteers received the vaccine intramuscularly (IM, or standard injection) or intradermally (ID) via the Mantoux technique. US researchers immunized 227 adults 18 to 49 years old with a Sanofi Pasteur H5N1 vaccine that was produced using methods similar to those used to manufacture Fluzone, a seasonal flu vaccine. The volunteers were randomly chosen to receive two doses 28 days apart either IM or ID. Although the vaccine contained 38.7 micrograms (mcg) of antigen (compared with 7.5 mcg for each of the three strains in Fluzone), immune responses were low: Only 25.4% in the IM group and 23.0% in the ID group achieved a fourfold or greater increase in antibody titer (measured by hemagglutination inhibition) 28 days after the first dose, and those percentages climbed to only 35.4% and 42.5%, respectively, after 56 days. Both delivery methods were well tolerated. The authors conclude, "Evaluation of higher dosages, alternative intradermal delivery methods, and the addition of adjuvants will be needed to enhance the immunogenicity of inactivated influenza A/H5N1 vaccines by the intradermal route."
Aug 13 J Infect Dis abstract