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Table 4 Estimates of the annual average and seasonal prevented fraction and number of averted influenza hospitalizations and deaths attributed to the vaccine program, for seasons 2014/15 to 2016/17

From: Impact of national influenza vaccination strategy in severe influenza outcomes among the high-risk Portuguese population

IRESeasonAverage
2014/152015/162016/17
Hospitalization
≥ 65 years
NAE (n) [95%CI]1124 [443–1863]1644 [460–2799]1957 [1326–2657]1584 [1058–2097]
PF (%)[95%CI]14.3 [6.2–21.6]24.3 [8.2–35.4]24.6 [18.1–30.7]21.0 [15.1–26.1]
NNV (n)[95%CI]890 [565–2233]621 [384–2050]616 [473–882]741 [553–1426]
< 65 years with chronic condition
NAE (n) [95%CI]222 [42–383]218 [106–326]311 [135–473]249 [158–337]
PF (%)[95%CI]15.6 [3.3–24.1]16.9 [9.1–23.4]23.2 [11.6–31.5]18.5 [12.5–23.4]
NNV (n) [95%CI]2657 [1628–10,924]2564 [1857–5172]2200 [1540–4957]2619 [1921–6015]
Deaths
≥ 65 years
NAE (n) [95%CI]409 [81-721]281 [52-489]427 [95-743]371 [198-541]
PF (%) [95%CI]27.7 [7.0-40.1]27.5 [6.7-40.1]31.9 [9.4-45.0]29.0 [18.0-37.4]
NNV (n) [95%CI]2416 [1459-10,267]3613 [2166-15,078]2796 [1633-10,422]3241 [1845-10,141]
< 65 years with chronic condition
NAE (n) [95%CI]13 [3–22]10 [2–49]12 [3–20]12 [6–16]
PF (%)[95%CI]18.9 [4.8–27.9]17.9 [4.3–26.1]22.0 [6.5–31.7]19.5 [11.8–25.4]
NNV (n)[95%CI]45,211 [29,413–176,520]54,149 [35,348–205,119]58,216 [37,146–206,237]57,230 [37,610–176,457]
  1. IRE influenza related event, NAE number of averted events, CI confidence interval, PF prevented fraction, NNV number needed to vaccinate
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