Safety of the Influenza A (H1N1)2009 Vaccine in Chronic Obstructive Pulmonary Disease: A Matched Case-Control Study

Background: The safety of influenza A (H1N1) 2009 among chronic obstructive pulmonary disease (COPD) patients has not been investigated yet. Our objective was to investigate the safety of the A (H1N1) 2009 vaccine, especially for mortality after vaccination. Methods: From October 2009 to March 2010, we collected records from all Japanese hospitals registered in the Japanese Respiratory Society. We conducted a 1:1 matched case-control study. Patients with COPD who died in the study period were determined as case group patients (n=36). Patients with COPD who survived the study period were determined as control group patients (n=36). In the control group selection process, we selected age, sex, period of home oxygen therapy (measure for COPD severity), hospital, and calendar time as matching factors. We then compared the proportion of patients who received the influenza A (H1N1) 2009 vaccine in each group and evaluated the conditional odds ratio. Results: Both the case and control groups had 36 COPD patients, 32 of whom were men. The mean age was 76.6 years (SD=8.6) in the case group and 76.9 years (SD=8.3) in the control group. The mean period of home oxygen therapy in both groups was 1.8. The proportion of patients receiving A (H1N1) 2009 vaccinations was 47.2% in the case group and 63.9% in the control group. The crude conditional odds ratio of mortality in the winter was 0.33 (95% confidence interval: 0.06-1.34) and adjusted conditional odds ratio was 0.37 (95% confidence interval: 0.09-1.52) with no significance. Conclusions: Our study detected no statistically increased risk of mortality after influenza A (H1N1) 2009 vaccination among COPD patients. The results are, however, limited by the small sample size and low statistical power. A similar larger-scale study is needed in the future to confirm our findings