Trends in Influenza Vaccine Uptake and Severe Influenza-Related Outcomes at Kaiser Permanente Southern California, 2007-2017.

INTRODUCTION

Major efforts to increase influenza vaccine uptake among Kaiser Permanente Southern California (KPSC) members have been undertaken in recent years. However, whether these improvements translate to a decline in severe influenza-related outcomes has not been examined. We aimed to understand the impact of the influenza vaccination program at KPSC by examining influenza vaccine uptake and 3 severe influenza-related outcomes.

METHODS

We conducted an ecologic trend analysis to understand influenza vaccine uptake and influenza-related hospitalization, intensive care unit (ICU) admission, and mortality for each influenza season (2007-2017). The same cohort was followed from the influenza season to the noninfluenza season immediately afterward while using the noninfluenza season as the comparison group. We also assessed the within-season correlation between influenza vaccine uptake and influenza-related outcomes.

RESULTS

Influenza vaccine uptake rose from 23.9% to 45.5%, and all 3 influenza-related outcome rates declined (hospitalization: 35.4-26.8/10,000 patients; ICU: 5.9-5.2/10,000 patients; and mortality: 3.4-2.3/10,000 patients). Influenza vaccine uptake was negatively correlated with hospitalization (-0.32, p < 0.001) and mortality (-0.29, p = 0.001). However, once we adjusted for the noninfluenza season, the results of the correlation analysis were no longer statistically significant.

CONCLUSION

Although we could not establish a statistically significant inverse relationship between influenza vaccination and severe influenza-related outcomes over the study period, our findings indicate an overall decline in influenza-related outcomes over the study period, suggesting improvements in both preventive and acute care quality at KPSC.