AGE AND TOLERANCE EFFECTS ON PNEUMOCOCCAL VACCINATION STRATEGIES IN THE ELDERLY. A COST-EFFECTIVENESS ANALYSIS

Background: Recent analyses suggest that ≥2 pneumococcal polysaccharide vaccine (PPV) doses in 50-year-old cohorts provide more protection from invasive pneumococcal disease (IPD) than single doses and are economically reasonable. The effects of multiple PPVs in older populations are unclear.

Methods: Using a Markov model, we separately estimated the cost-effectiveness of single- and multiple-dose PPV strategies in 65-, 75-, and 80-year-old cohorts. National Health Interview Survey data were used to segment cohorts by comorbidity. Age- and comorbidity-specific invasive pneumococcal disease (IPD) rates were obtained from the CDC. IPD costs were obtained from HCUP and utilities from the medical literature; an expert panel estimated PPV-related protection from IPD based on age, comorbidity, and time since vaccination. Costs (in 2003 US$) and effectiveness were from the societal perspective and discounted 3%/yr. One-way and probabilistic sensitivity analyses were performed. In base case analyses we assumed no prior PPV; in sensitivity analyses we examined the possible effects of prior vaccination and of tolerance (decreased effectiveness of subsequent PPVs).

Results: Incremental cost-effectiveness ratios (ICER) for non-dominated strategies in each age cohort are summarized below. A single PPV at age 65 was economically reasonable, while vaccinations at ages 75 and 80 were more expensive, particularly when multiple vaccination strategies were considered. Results were most sensitive to individual variation of vaccine effectiveness estimates. Probabilistic sensitivity analyses, where parameters were simultaneously varied over distributions 3000 times, supported baseline results. When we assumed both prior vaccination and 80% effectiveness of subsequent PPVs, base case ICERs increased by 29-34% for single dose strategies and 37-133% for strategies with multiple subsequent PPVs.

Conclusion: Depending on the cost-effectiveness acceptability threshold, single dose PPV strategies are worth considering for IPD prevention for patients aged 65-80 from clinical and economic standpoints. Multiple PPV strategies are more expensive, particularly when prior vaccination and the possibility of vaccine tolerance are considered.

Cohort age	Vaccination age	ICER
65	65	$26,100
	65 75	$88,400
	65 70 75 80	$188,000
75	75	$71,300
	75 85	$92,700
80	80	$75,800
	80 85	$548,000