Human vaccination for avian influenza viruses has not been widely used, although multiple vaccination trials are underway. Prior avian vaccines in humans have been poorly immunogenic and thus have limited use. An inactivated H5N3 has been tested and was tolerated but with limited immunogenicity [91, 92] . Other H5 vaccines have resulted in the development of neutralizing antibodies, but to a limited degree [93, 94] . Recently, a large randomized trial looked at an H5N1 attenuated vaccine from the Vietnam strain [95] . Only a modest immune response was seen, with microneutralization antibodies being developed at 12 times the dose used in the seasonal influenza vaccine. The side effects were minimal. A number of other industry trials with adjuvant vaccines are currently ongoing. Although promising, human vaccination against avian influenza viruses is still under development. Underscoring this development is the uncertainty of a pandemic strain, which may have vastly different antigenic properties from any developed H5 vaccine.