Cost-effectiveness of stockpiling 23-valent pneumococcal polysaccharide vaccine to prevent secondary pneumococcal infections among a high-risk population in the United States during an influenza pandemic.

BACKGROUND Secondary bacterial infections (especially pneumococcal infections) were a major cause of death during prior influenza pandemics. One strategy to prevent pneumococcal infections in adults during a future pandemic is to stockpile 23-valent pneumococcal polysaccharide vaccine (PPSV23). Stockpiling a pneumococcal vaccine can ensure that it is available when needed most-that is, at the onset of a pandemic. OBJECTIVE The purpose of this article was to project the health and economic impact of stockpiling PPSV23 to prevent secondary pneumococcal infections among high-risk adults aged 18 to 64 years during an influenza pandemic within the United States. METHODS A cost-effectiveness model was developed to evaluate the health and economic effects of stockpiling PPSV23 versus not stockpiling this vaccine for preventing secondary pneumococcal infections among 20 million high-risk US adults aged 18 to 64 years during an influenza pandemic. The model was used to project the number of pneumococcal cases, hospitalizations, deaths, and days of work loss averted. Three health outcomes (deaths, hospitalizations, and outpatient care) were estimated from secondary pneumococcal infections. To assess the overall effectiveness of the different strategies, the quality-adjusted life-year (QALY) was used as a measure of these 3 health outcomes. The results are presented for 3 scenarios based on the pandemic severity and anticipated prepandemic influenza vaccine availability: base case, more-severe case, and less-severe case. RESULTS In the base-case scenario, vaccinating 20 million high-risk adults with PPSV23 avoided 2858 deaths, 878 hospitalizations, 41,881 pneumococcal pneumonia cases, and 232,891 days of work loss during a pandemic. Under the more-severe case scenario, vaccination avoided 21,921 deaths, 10,280 hospitalizations, 70,345 pneumococcal cases, and approximately 1.12 million days of work loss. Under the less-severe case scenario, pneumococcal vaccination avoided 715 deaths, 219 hospitalizations, 10,470 pneumococcal cases, and 58,235 days of work loss. The incremental cost-effectiveness ratio for stockpiling PPSV23 versus no stockpiling for the base-case and less-severe case scenarios was $39,946 and $198,653 per QALY, respectively. For the more-severe case scenario, stockpiling PPSV23 was cost saving. Probabilistic sensitivity analyses found that the range of incremental cost-effectiveness ratio values was broad due to the large uncertainty regarding the timing and impact of the next pandemic. In addition, the shelf life of PPSV23 and stockpile management substantially influenced the cost-effectiveness ratio. CONCLUSIONS For severe pandemics or pandemics in which prepandemic influenza vaccine is unavailable, stockpiling of PPSV23 can be a cost-effective strategy for reducing the health and economic burden associated with secondary pneumococcal infections in a high-risk US population. However, for a mildly severe pandemic in which prepandemic influenza vaccine is available, stockpiling of PPSV23 may not be cost-effective.