| Summary: | Influenza vaccination is the best preventive measure against influenza virus infection, and antivirals including oseltamivir are effective treatments. From a public health point of view, it is important to evaluate whether vaccination and antiviral treatment reduces transmission of the virus. I analyzed data from a community-based study of influenza virus transmission in households, and identified effectiveness of antiviral treatment in reducing duration of illness and some evidence that treatment reduced transmission to household contacts. I also analyzed data from a community-based placebo-controlled trial of influenza vaccination and confirmed efficacy of vaccination against seasonal influenza but differential efficacy against pandemic influenza possibly because of timing and mediation of seasonal influenza epidemics. In further analyses I found that antibody titers of 1:40 correlated with 50% protection against infection, and repeated vaccination with the same strains tended to be associated with reduced responses to those strains although there was no evidence of reduced efficacy. In the study, one child in each household was randomly allocated to receive vaccine or placebo and I did not identify any evidence of indirect benefits to the household members of vaccinated children. I reviewed vaccine target groups in different countries, and noted that some countries now include school-age children in their target groups based mainly on the principle of herd immunity. My findings did not support the inclusion of school-age children as a target group for vaccination in Hong Kong. Further studies should examine the indirect as well as direct benefits of vaccination in different settings in order to guide optimal influenza vaccination policies. === published_or_final_version === Community Medicine === Doctoral === Doctor of Philosophy
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