MF59-adjuvanted and virosomal influenza vaccines for preventing influenza hospitalization in older people: comparative effectiveness using the Valencia health care information system.

BACKGROUND: Adjuvanted influenza vaccines offer greater and broader immunogenicity to older adults than conventional vaccines. Studies assessing the comparative effectiveness of adjuvanted influenza vaccines in this age group are lacking.
METHODS: We conducted a retrospective cohort study to estimate the comparative effectiveness of MF59-adjuvanted trivalent influenza vaccine (TIV) and virosomal-TIV for prevention of influenza hospitalization in adults aged ≥65 years. We obtained administrative data on immunization status and influenza hospitalization for the 2010-2011 influenza season. We used Cox regression models to assess comparative effectiveness; crude and adjusted by age, sex, comorbidity, deprivation, type of insurance, and travel time to hospital. We accounted for data clustering at the hospital level by using a multilevel random effects model.
RESULTS: Overall, 373,798 vaccinated subjects were evaluated. There were 40 hospitalizations for influenza among 176,618 subjects, contributing 4,288,109 person-weeks at risk in the virosomal-TIV group, and 37 hospitalizations for influenza among 197,180 subjects, contributing 4,786,360 person-weeks at risk in the MF59-TIV group. The crude hazard ratio (HR) was 0.83 (0.53-1.30), and the adjusted Cox estimated HR of MF59-TIV relative to virosomal-TIV was 0.86 (0.55-1.35). After accounting for data clustering, the HR of influenza hospitalization associated with MF59-TIV relative to virosomal-TIV was 0.94 (0.37-2.38).
CONCLUSION: During the 2010-2011 influenza season, we found no differences in the risk of influenza hospitalization in subjects aged ≥65 years vaccinated with MF59-TIV compared with those vaccinated with virosomal-TIV.