The effectiveness of shingles vaccine among Albertans aged 50 years or older: A retrospective cohort study.

Purpose: We assessed the effectiveness of shingles vaccine in preventing incident shingles among Alberta residents aged 50 years or older over the period 2009 - 2015, using administrative health data.

Methods: The cohort comprised of Albertans from the Alberta Health Care Insurance Plan Registry (AHCIP) as of June 30, 2009 and aged 50 years or older. Those who received shingles vaccine were identified from the provincial pharmaceutical information network. The occurrence of incident shingles was identified through both inpatient and outpatients/community care data. Incident shingles was defined as the earliest dated record of ICD 9-CM 053 or ICD-10-CA B02. Starting on November 1, 2009, individuals with no history of shingles or shingles vaccination were followed until Nov 1, 2015 (6 years), or until shingles incidence, death, or AHCIP cancellation (including leaving Alberta). Vaccine effectiveness (VE) was estimated as the inverse of the relative risk of developing incident shingles in each year following vaccination compared to time at risk without vaccination, while adjusting for age, sex, income quintile, and immune compromising conditions (identified from physician claims, inpatient, and cancer registry data).

Results: There were 1,094,236 individuals in the cohort, with 85,439 (7.80%) vaccinated individuals. The shingles incidence rate was 9.03 [95% CI: 8.95, 9.11] cases per 1,000 person years (49,243 cases). Adjusted VE in the first year following immunization was 50.02% [95% CI: 44.71%, 54.83%] against incident shingles, decreasing to no effect by the fifth year (VE = 14.00% [95% CI: -20.99%, 38.88%]).

Conclusions: Our findings are consistent with observations from other population based studies and provide population level data for policy-makers to review when making decisions related to public funding of shingles vaccine.