Economic Analysis of Pre-pandemic Influenza Vaccination Strategies in Singapore

Presenter: Mei Yin Tok, University of Singapore

Abstract

The rapid spread of H5N1 avian influenza A viruses from Asia to Middle East, Europe and Africa has enabled these viruses to be deeply entrenched in the ecosystem. Although H5N1 is currently a prime contender as the most likely pandemic strain, no one knows when and what strain will trigger the next influenza pandemic. Recently, an additional option besides pandemic preparedness plans and stockpiling on antiviral drugs including oseltamivir, has emerged in the form of H5N1 vaccines which have been touted as a possible strategy of pre-pandemic protection against a future pandemic if it is caused by a H5N1 strain (2,3). Following successful clinical trials, such vaccines are currently available and some countries have even begun stockpiling them for use in an emergency. Although these vaccines provide another dimension to pandemic preparedness for policy makers, the cost-effectiveness of such a strategy is unknown.

We analyzed the economic outcomes of pre-pandemic vaccination compared with treatment with anti-viral agents only in Singapore using a decision-based model to perform cost-benefit and cost-effectiveness analyses. The analyses also provide the optimal strategies and investments for vaccines depending on the vaccine efficacy and other key parameters. As a future influenza pandemic is unpredictable with many uncertainties about the outcomes, we have modeled all uncertain input variables as triangular distributions centered on base values, with ranges based on the minimum and maximum plausible values derived from previous studies. Analyses were performed based on the key outcomes of overall cost-benefit, cost per life saved, and the break-even cost for the vaccine where the cost-benefit for the two strategies is similar. The break-even cost includes all costs associated with vaccination including research and development by the country, purchase cost, shelf-life extensions and additional stockpiles, administration, and adverse effects.

The treatment-only strategy resulted in 350 to 1,122 deaths and SGD$427 to SGD$1,965 million in costs. At a vaccine cost of SGD$70, vaccination increased cost-benefit by SGD$28 to 79 million and reduced deaths by 22 to 69 for every 10% increase in vaccine efficacy. Under most conditions, vaccination is cost-beneficial for all high-risk groups. Higher attack rates and higher case-fatality rates resulted in higher break-even vaccination costs. At case-fatality rates of >1.2%, vaccination is always cost-beneficial in all Monte Carlo simulation iterations. As the actual vaccine efficacy level and time to a pandemic is unknown, the decision to stockpile will be based on perception of disease severity. Policy makers considering vaccine stockpiling as insurance against worst-case scenarios will find it cost-effective.