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BACKGROUND: In the elderly, traditional influenza inactivated vaccines are often only modestly immunogenic, owing to immunosenescence. Given that adjuvantation is a means of enhancing the immune response, the trivalent inactivated vaccine adjuvanted with MF59 (MF59-TIV) was specifically designed to overcome this problem. Considering that, for ethical reasons, the absolute effectiveness of an influenza vaccine in the elderly cannot be demonstrated in placebo-controlled studies, the present study aimed to assess the effectiveness of MF59-TIV in preventing influenza-related outcomes in the elderly. METHODS: We conducted a systematic review of observational studies aimed at evaluating the effectiveness of MF59-TIV against influenza-related outcomes. Results of single studies were pooled whenever possible. RESULTS: Of the 1993 papers screened, 11 (6 case-control, 3 cohort and 2 prospective case-control) studies were identified. Hospitalization due to pneumonia/influenza and laboratory-confirmed influenza were reported in more than one study, while other outcomes (influenza-like illness, cardio- and cerebrovascular accidents) were investigated only by one study each. Pooled analysis of four case-control studies showed an adjusted MF59-TIV effectiveness of 51% (95% CI: 39-61%) against hospitalizations for pneumonia/influenza among community-dwelling seniors. Pooled results of the adjusted vaccine effectiveness against laboratory-confirmed influenza were also high (60.1%), although the 95% CI passed through zero (-1.3 to 84.3%). Other single community-based studies showed very high effectiveness of MF59-TIV in preventing hospitalizations for acute coronary 87% (95% CI: 35-97%) and cerebrovascular 93% (95% CI: 52-99%) events. MF59-TIV proved highly effective 94% (95% CI: 47-100% in reducing influenza-like illness among institutionalized elderly. Furthermore, MF59-TIV displayed greater efficacy than non-adjuvanted vaccines in preventing hospitalizations due to pneumonia/influenza adjusted risk ratio 0.75 (95% CI: 0.57-0.98) and laboratory-confirmed influenza adjusted odds ratio 0.37 (0.14-0.96). CONCLUSIONS: Our results suggest that MF59-TIV is effective in reducing several influenza-related outcomes among the elderly, especially hospitalizations due to influenza-related complications.
Domnich et al. (Fri,) studied this question.