Association between monovalent influenza A (H1N1) pdm09 vaccine and pneumonia among the elderly in the 2009–2010 season in Japan: A case-control study

Abstract

Abbreviations: H1N1pdm, monovalent influenza A (H1N1) pdm09; TIV, trivalent seasonal influenza vaccine; COPD, chronic obstructive pulmonary disease; ADL, activities of daily living; OR, odds ratio; CI, confidence interval.We investigated the association between monovalent influenza A (H1N1) pdm09 (H1N1pdm) vaccine and pneumonia in elderly people. Study design was a hospital-based, matched case-control study. Cases comprised patients 65 years old who had been newly diagnosed with pneumonia. For each case, 2 controls were defined as individuals with other diseases (not pneumonia) who were matched by sex, age, entry date, and the visited hospital. Study period was the interval from 1 September 2009 until 30 September 2010. Because a pandemic of influenza A (H1N1) occurred during study period, we analyzed selected subjects who had enrolled during the influenza A (H1N1) pandemic. We calculated the odds ratios (ORs) and 95% confidence intervals (CIs) for pneumonia in H1N1pdm-vaccinated subjects compared with unvaccinated subjects using a conditional logistic regression model to assess the association between H1N1pdm vaccine and pneumonia. The subjects during the period of the influenza A (H1N1) pandemic were 20 cases and 40 controls. Subjects who had received H1N1pdm vaccine showed a significantly decreased OR for pneumonia (OR D 0.10, 95% CI D 0.01-0.98) compared with unvaccinated subjects. In conclusion, H1N1pdm vaccination may have prevented pneumonia among the elderly during the 2009-2010 influenza A (H1N1) pandemic in Japan.

Preventive effects of pneumococcal and influenza vaccines on community-acquired pneumonia in older individuals in Japan: a case-control study

“…33,34 Consequently, we defined patients who had received the vaccine within the past 5 years as "vaccinated". 36 All underlying diseases were classified into "present vs. absent", and ADL was classified into "non-self-supported (bedridden, semibedridden, or semi-self-supported) vs. self-supported" for analyses. BMI was calculated as weight in kilograms (kg) divided by the square of height in meters (m 2 ), and BMI was categorized into 3 levels (<18.5, 18.5-24.9, and ≥25.0).…”