Intradermal and virosomal influenza vaccines for preventing influenza hospitalization in the elderly during the 2011-2012 influenza season: a comparative effectiveness study using the Valencia health care information system.

BACKGROUND: The use of intradermal vaccination or virosomal vaccines could increase protection against influenza among the vulnerable population of older adults. Studies assessing the comparative effectiveness of these two influenza vaccine types in this age group are lacking. METHODS: We conducted a retrospective cohort study to estimate the comparative effectiveness of intradermal seasonal trivalent-influenza vaccine (TIV) delivered by a microneedle injection system and a virosomal-TIV intramuscularly delivered for prevention of influenza hospitalization in non-institutionalized adults aged ≥65 years. We obtained administrative data on immunization status and influenza hospitalization for the 2011-2012 influenza season, and used Cox regression models to assess comparative effectiveness. We estimated crude and adjusted (age, sex, comorbidity, pharmaceutical claims, recent pneumococcal vaccination and number of hospitalizations for all causes other than influenza between the previous and current influenza seasons) hazard ratios (HR). RESULTS: Overall, 164,021 vaccinated subjects were evaluated. There were 127 hospitalizations for influenza among 62,058 subjects, contributing 914,740 person-weeks at risk in the virosomal-TIV group, and 133 hospitalizations for influenza among 101,963 subjects, contributing 1,504,570 person-weeks at risk in the intradermal-TIV group. The crude HR of intradermal-TIV relative to virosomal-TIV was 0.64 (95% confidence interval (CI): 0.50-0.81), and the adjusted Cox estimated HR was 0.67 (95% CI: 0.52-0.85). CONCLUSIONS: During the 2011-2012 influenza season the risk of hospitalization for influenza was reduced by 33% in non-institutionalized elderly adults who were vaccinated with intradermal-TIV compared with virosomal-TIV.

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.