Preventing the Risk of Hospitalization for Respiratory Complications of Influenza among the Elderly: Is There a Better Influenza Vaccination Strategy? A Retrospective Population Study

Abstract

<jats:p>Influenza and its complications are an important public health concern, and vaccination remains the most effective prevention measure. However, the efficacy of vaccination depends on several variables, including the type of strategy adopted. The goal of this study was to assess the impact of different influenza vaccination strategies in preventing hospitalizations for influenza and its related respiratory complications. A retrospective cohort study was conducted on data routinely collected by the health services for six consecutive influenza seasons, considering the population aged 65 years or more at the time of their vaccination and living in northeastern Italy. Our analysis concerns 987,266 individuals vaccinated against influenza during the study period. The sample was a mean 78.0 ± 7.7 years old, and 5681 individuals (0.58%) were hospitalized for potentially influenza-related reasons. The hospitalization rate tended to increase over the years, not-significantly peaking in the 2016–2017 flu season (0.8%). Our main findings revealed that hospitalizations related to seasonal respiratory diseases were reduced as the use of the enhanced vaccine increased (R2 = 0.5234; p &lt; 0.001). Multivariate analysis confirmed the significantly greater protective role of the enhanced vaccine over the conventional vaccination strategy, with adjusted Odds Ratio (adj OR) = 0.62 (95% CI: 0.59–0.66). A prior flu vaccination also had a protective role (adj OR: 0.752 (95% CI: 0.70–0.81)). Age, male sex, and H3N2 mismatch were directly associated with a higher risk of hospitalization for pneumonia. In the second part of our analysis, comparing MF59-adjuvanted trivalent inactivated vaccine (MF59-TIV) with conventional vaccines, we considered 479,397 individuals, of which 3176 (0.66%) were admitted to a hospital. The results show that using the former vaccine reduced the risk of hospitalization by 33% (adj OR: 0.67 (95% CI: 0.59–0.75)). This study contributes to the body of evidence of a greater efficacy of enhanced vaccines, and MF59-adjuvanted TIV in particular, over conventional vaccination strategies in the elderly.</jats:p>

Effectiveness of the MF59‐adjuvanted trivalent or quadrivalent seasonal influenza vaccine among adults 65 years of age or older, a systematic review and meta‐analysis

“…The 26 records included in the review covered 21 studies in total: seven test‐negative case‐control studies (with eight records), 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 five case‐control studies, 33 , 34 , 35 , 36 , 37 eight cohort studies (with ten records), 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 and one cluster‐randomized trial (with three records). 48 , 49 , 50 All studies were conducted in North America and Europe during the 2006/07–2019/20 influenza seasons.…”

“…Eight studies used administrative data sources for medical care (clinic, ED, or hospital visits) to assess the effectiveness of aTIV relative to other influenza vaccines. Three of the studies were conducted in Italy using hospital catchment areas or OP rosters 38 , 41 , 42 and five studies were conducted in the USA using Medicare 39 , 40 or other medical and pharmacy claims‐based information and medical records. 44 , 45 , 46 , 47 , 51 These studies were conducted in the 2006/07 through 2018/19 influenza seasons.…”

“…Izurieta et al studied non-institutionalized Medicare beneficiaries of whom 40% had underlying heart disease, 30% had diabetes mellitus, and 45% were on home oxygen, for instance. In comparison, Pelton et al 44 39 Cocchio et al, 42 and Mannino et al 41 restricted their analyses to peak periods of influenza activity, for example. In the absence of other potential sources of bias, it is expected that restricting to a period of higher influenza activity would increase the specificity of the outcome definition resulting in a more accurate, but potentially less precise, estimate due to reduction in sample size.…”

“…As shown in Figure 4A, the pooled relative VE estimate showed a benefit of aTIV relative to TIV at 13.9% (4.2, 23.5) but with considerable heterogeneity (I 2 = 95.9%, p < 0.01). 39,41,42,44,47 The relative VE of aTIV compared to QIV ranged from −6.6% to 36.3% with a pooled estimate of 13.7% (3.1, 24.2; I 2 = 98.8%, p < 0.01), indicating a benefit of aTIV over QIV 39,40,44,47 (Figure 4B). The relative VE comparing aTIV to HD-TIV for reducing any medical encounters due to influenza and/or pneumonia ranged from −14.9% to 16.6% in five studies.…”

“…The 26 records included in the review covered 21 studies in total: seven test-negative case-control studies (with eight records), [25][26][27][28][29][30][31][32] five case-control studies, [33][34][35][36][37] eight cohort studies (with ten records), [38][39][40][41][42][43][44][45][46][47] and one cluster-randomized trial (with three records). [48][49][50] All studies were conducted in North America S2).…”