Background. The Shingles Prevention Study (SPS; Department of Veterans Affairs Cooperative Study 403) demonstrated that zoster vaccine was efficacious through 4 years after vaccination. The Short-Term Persistence Substudy (STPS) was initiated after the SPS to further assess the persistence of vaccine efficacy. Methods. The STPS re-enrolled 7320 vaccine and 6950 placebo recipients from the 38 546-subject SPS population. Methods of surveillance, case determination, and follow-up were analogous to those in the SPS. Vaccine efficacy for herpes zoster (HZ) burden of illness, incidence of postherpetic neuralgia (PHN), and incidence of HZ were assessed for the STPS population, for the combined SPS and STPS populations, and for each year through year 7 after vaccination. Results. In the STPS as compared to the SPS, vaccine efficacy for HZ burden of illness decreased from 61.1 to 50.1, vaccine efficacy for the incidence of PHN decreased from 66.5 to 60.1, and vaccine efficacy for the incidence of HZ decreased from 51.3 to 39.6, although the differences were not statistically significant. Analysis of vaccine efficacy in each year after vaccination for all 3 outcomes showed a decrease in vaccine efficacy after year 1, with a further decline thereafter. Vaccine efficacy was statistically significant for the incidence of HZ and the HZ burden of illness through year 5. Conclusions. Vaccine efficacy for each study outcome was lower in the STPS than in the SPS. There is evidence of the persistence of vaccine efficacy through year 5 after vaccination but, vaccine efficacy is uncertain beyond that point.
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Acknowledgments. The study was conducted by the Cooperative Studies Program, Department of Veterans Affairs, Office of Research and Development. Additional support was provided by the National Institute of Allergy and Infectious Diseases, Merck, and the James R. and Jesse V. Scott Fund for Shingles Research. Data management and analysis support was provided at West Haven Cooperative Studies Program Coordinating Center by K. Dellert and K. Newvine. Statistical assistance at Merck was provided by W. W. B. Wang.
Financial support. This work was supported by funding from VA CSP 403 and a grant from Merck to the VA Cooperative Studies Program and, subsequently, to the Veterans Medical Research Foundation and the VA Connecticut Research and Education Foundation.
Potential conflicts of interest. P. M. K., L. X., P. A., and I. C. are employees of Merck. K. E. S. has received grant support from Merck. M. L. has received grant support, consulting fees, and royalties from Merck and grant support and consulting fees from GlaxoSmithKline. S. K. serves on a Merck data safety monitoring board. V. M. has received consulting and speaker fees. All other authors report no potential conflicts.