Moreover, due to paucity of data, our model was not able to estimate the proportion of open vial wastage due to contamination, exposure to extreme temperatures and improper administration techniques. For these reasons,

the wastage rates yielded in our model are conservative estimates. Another potential limitation of this paper is that our model did not capture the impact of vaccine vial size on the coverage rate. Vaccine policy makers may encounter a concern that the choice of vial size could affect vaccine coverage due to a HCW’s fear of opening a new vial. For example, in the event Angiogenesis inhibitor that an eleventh child shows up toward the end of a vaccination session, it is possible that a HCW will be less reluctant to open a 5-dose vial than a 10-dose vial. If the clinic was equipped with only 10-dose vials, some staff might prefer to reschedule a vaccination to avoid wastage, and thus take a risk that the child will not return [21]. Additionally, the model assumed that 5-doses of vaccine are packaged in a slightly smaller vial size compared to

10-doses of vaccine, when it is possible that the actual size of the vial does not change depending on the dose. Furthermore, we did not take into account micro VX 770 cold chain costs in our model, including the cost to buy and/or run additional refrigerators. These two prior assumptions could have led to an underestimation of cold chain costs. Moreover, we assumed that the whole country was using the same vial size when we modeled open vial wastage, and did not examine possibilities of choosing a combination of 10-, 5-, and single-dose vials. Finally, we designed a dynamic model based on Lee’s methodology and populated it with field data, which can enable decision-makers in the four countries to simulate different vaccination scenarios. The negative binomial distribution was typically the best fitting distribution by the Akaike Information Criteria; however when we compared results using Poisson as the distribution pattern with parameters generated from @Risk in each country, the

estimated vial wastage did not vary much. In no case did the choice of arrival distribution alter the identification of the most cost-effective many choice of wastage control strategy. Our ongoing research is exploring the mathematical reason why models of open-vial wastage are relatively insensitive to the assumptions about arrival distribution. The current results confirm that collecting detailed data on the arrival distribution is primarily useful to achieve precise estimates of expected wastage, but identifying the most cost-effective vial size strategy is not sensitive to assumptions within the choices of Poisson, or negative binomial distribution. In summary, our study found that open vial wastage can be lowered by reducing MDVs from 10-dose vials to 5-dose vials.