COST-EFFECTIVENESS OF COMBINED INFLUENZA AND PNEUMOCOCCAL VACCINATION: IS IT THE RIGHT TIME?

Purpose: Invasive pneumococcal disease (IPD) causes significant morbidity and mortality in pandemic influenza. Influenza vaccination is now recommended for all ages; pneumococcal polysaccharide vaccination (PPV) is recommended in patients <65 only when comorbidities are present. Prior analyses, showing relative cost-effectiveness of each vaccine separately at age 50, suggest that giving both vaccines could be considered in all patients aged ≥50.   

Method: We constructed a Markov model to estimate the incremental cost-effectiveness of 5 vaccination strategies in 50-year-old US population cohorts: no vaccination, influenza vaccination only, PPV only, vaccinate all with both vaccines, and a Centers for Disease Control and Prevention (CDC) recommendation strategy (influenza vaccination for all, PPV when comorbid conditions are present). The cohort was followed for 10 years, with differing time horizons examined in sensitivity analyses. Costs were 2006 US$, discounting costs and effectiveness 3%/yr. An expert panel estimated PPV effectiveness; other probabilities and utilities were estimated from published sources and CDC data; costs were from the medical literature and National Inpatient Survey data. We assumed yearly influenza vaccination with 80% protection, 10% annual influenza incidence, 3.3% influenza hospitalization risk, and 10% IPD risk in hospitalized influenza patients. Parameter values were examined in 1-way, multi-way, and probabilistic sensitivity analyses.

Result: No vaccination and either individual vaccination were dominated by the CDC recommendation strategy. Compared to CDC recommendations, dual vaccination for all cost $9.20 more while gaining 0.00025 QALYs (~0.1 days), or $37,700/QALY gained. Results were most sensitive to model time horizon variation, with the incremental cost-effectiveness ratio (ICER) of dual vaccination for all >$100K/QALY if the time horizon was ≤6 years. In probabilistic sensitivity analyses, dual vaccination for all was favored at an acceptability threshold of $100K in 6.2% of model iterations at a 5-year time horizon and 97.5% at 10 years. Offering both vaccinations for all cost $5,300/QALY when age- and comorbidity-based vaccination coverage (base case: 100% for both) was changed to observed rates (57.1% and 32.5% respectively).  

Conclusion: Dual vaccination of 50-year-olds, regardless of comorbidity status, is clinically and economically reasonable, particularly given heightened IPD risk during the current influenza pandemic. Models considering relatively short time horizons, which do not account for longer-term PPV effectiveness, will overestimate the ICER of combined vaccination strategies.