Cost-effectiveness of influenza vaccination in prior pneumonia patients in Israel

Abstract

Pneumonia is a common complication of influenza infection, and accounts for the majority of influenza mortality. Both the WHO and the Ministry of Health in Israel prioritize seasonal influenza vaccination primarily on the basis of age and specific co-morbidities. Here we consider whether the targeting of individuals previously infected with pneumonia for influenza vaccination would be a cost-effective addition to the current policy. We performed a retrospective cohort data analysis of 163,990 cases of pneumonia hospitalizations and 1,305,223 cases of outpatient pneumonia from 2004 to 2012, capturing more than 54% of the Israeli population. Our findings demonstrate that patients infected with pneumonia in the year prior had a substantially higher risk of becoming infected with pneumonia in subsequent years (relative risk >2.34, p<0.01). Results indicated that the benefit of targeting for influenza vaccination patients hospitalized with pneumonia in prior year would be cost-saving regardless of age. Complementing the current policy with the targeting of prior pneumonia patients would require vaccination of only a further 2.3% of the Israeli population to save additional 204-407 quality-adjusted life years (QALYs) annually at a mean price of 58-1056 USD/QALY saved. Global uncertainty analysis demonstrates that the cost-effectiveness of adding this policy is robust over a vast range of conditions. As prior pneumonia patients are currently not prioritized for influenza vaccination in Israel, nor elsewhere, this study suggests a novel supplement of current policies to improve cost-effectiveness of influenza vaccination. Future studies should use case-control study to further evaluate the effectiveness of vaccination in prior pneumonia patients.

Keywords: Cost-effectiveness; Influenza and pneumonia; Influenza vaccination.

Figure 1

Mean relative risk of infection given illness in k^th prior season in the four scenarios, distinguishing between outpatient treatment and hospitalization. Dash lines reflect the lower bound above which the prior season’s patients risk is higher than others, adjusting for the effect of age, and a reference line in which the relative risk equals one. 95% Confidence intervals between years performed under the assumption of normal distribution.

Figure 2

(A) Costs and QALYs saved given the implementation of target groups in optimal order of prioritization (B) Corresponding additional vaccination coverage on top of the current policy (C) Willingness to pay per QALY saved for each vaccination program. The vaccination programs ranked by cost-effective order are A) Targeting P_H patients and P_O outpatients >65 B) Targeting additionally prior P_O 50–65 C) Targeting additionally prior P_O 0–4 D) Targeting additionally prior P_O 25–50 E) Targeting additionally prior P_O 4–25.

Figure 3

Probabilities in which targeting P_O and P_H in each age-group is cost-effective given level of willingness to pay per QALY in ages A) 0–4 B) 4–25 C) 25–50 D) 50–65 E) >65 relative to the current policy. The vertical dashed line reflects the 2012 GDP per capita, (i.e. 32,000$).