title: Effectiveness of MF59-adjuvanted seasonal influenza vaccine in the elderly: A systematic review and meta-analysis.
abstract: 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.
  
  
  
  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.
  
  
  
  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)].
  
  
  
  Our results suggest that MF59-TIV is effective in reducing several influenza-related outcomes among the elderly, especially hospitalizations due to influenza-related complications.
authors.affiliation: Department of Health Sciences, University of Genoa, Genoa, Italy.
authors.forename: Alexander
authors.initials: A
authors.lastname: Domnich
authors.affiliation: Department of Health Sciences, University of Genoa, Genoa, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Arata
authors.affiliation: Department of Health Sciences, University of Genoa, Genoa, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Amicizia
authors.affiliation: Vaccines Research Unit, FISABIO-Public Health, Valencia, Spain.
authors.forename: Joan
authors.initials: J
authors.lastname: Puig-Barberà
authors.affiliation: Department of Health Sciences, University of Genoa, Genoa, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Gasparini
authors.affiliation: Department of Health Sciences, University of Genoa, Genoa, Italy. Electronic address: panatto@unige.it.
authors.forename: Donatella
authors.initials: D
authors.lastname: Panatto
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage*; D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000517:prevention & control*; D064887:Observational Studies as Topic; D011136:Polysorbates / Q000008:administration & dosage*; D013185:Squalene / Q000008:administration & dosage*; D016896:Treatment Outcome; D015164:Vaccines, Inactivated / Q000008:administration & dosage / Q000276:immunology
chemical_list: D000276:Adjuvants, Immunologic; D007252:Influenza Vaccines; C089950:MF59 oil emulsion; D011136:Polysorbates; D015164:Vaccines, Inactivated; D013185:Squalene
keywords: Elderly; Influenza vaccine; Influenza vaccine effectiveness; MF59-adjuvanted vaccine; Meta-analysis