HZ/su was more reactogenic than placebo. Among HZ/su recipients, 81.5% had injection-site reactions, and 66.1% had systemic reactions. The most frequent reactions were pain at the injec- tion site and myalgia, findings that are consistent with the results of phase 1–2 studies.19,21-24 Previous studies suggest that the antigen and the adjuvant both contribute to the difference in solicited injection-site and systemic reactions.17,21 However, reactions were transient and mostly of mild-to-moderate intensity, and the fact that approximately 96% of the participants in the HZ/su and placebo groups received two doses of the study vaccine suggests that the reactogenicity of the HZ/su vaccine did not greatly affect par- ticipants’ willingness to receive the second dose.