Effectiveness of inactivated influenza vaccine against laboratory-confirmed influenza pneumonia among adults aged ≥65 years in Japan

Publication date: 17 May 2018
Source:Vaccine, Volume 36, Issue 21
Author(s): Motoi Suzuki, Naoko Katsurada, Minh Nhat Le, Norihiro Kaneko, Makito Yaegashi, Naoto Hosokawa, Yoshihito Otsuka, Masahiro Aoshima, Lay Myint Yoshida, Konosuke Morimoto
BackgroundThe effectiveness of inactivated influenza vaccine (IIV) against laboratory-confirmed influenza pneumonia in older adults remains to be established.MethodsPneumonia patients aged ≥65 years who visited a study hospital in Chiba, Japan, were prospectively enrolled from February 2012 to January 2014. Sputum samples were collected from participants and tested for influenza virus by polymerase chain reaction assays. Influenza vaccine effectiveness (IVE) against laboratory-confirmed influenza pneumonia was estimated by a test-negative design.ResultsAmong a total of 814 pneumonia patients, 42 (5.2%) tested positive for influenza: 40 were positive for influenza A virus, and two were positive for influenza B virus. The IVE against laboratory-confirmed influenza pneumonia was 58.3% (95% confidence interval, 28.8–75.6%). The IVE against influenza pneumonia hospital admission, severe pneumonia, and death was 60.2% (95% CI, 22.8–79.4%), 65.5% (95% CI, 44.3–78.7%), and 71% (95% CI, −62.9% to 94.8%), respectively. In the subgroup analyses, the IVE against influenza pneumonia was higher for patients with immunosuppressive conditions (85.9%; 95% CI, 67.4–93.9%) than for those without (48.7%; 95% CI, 2.7–73%) but did not differ by patients' statin use status.ConclusionIIV effectively reduces the risk of laboratory-confirmed influenza pneumonia in older adults.



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