Carla,
This is indeed an interesting topic. and the answer is not trivial. The problem is that closed vial wastage is hardly ever reported separately, because there is often an element of neglect or error involved, and people would rather not report on their errors. It thus becomes hard to determine what percentage of wastage would be caused by, say, vaccine expiry, VVM exposure or freezing. But in some cases, total wastage is available (as the difference between used vaccine and the reported number of administered doses). The question now is: what part of this total wastage is attributable to closed vial wastage versus open vial wastage. The latter is a more acceptable kind of wastage as it is not caused by a weak supply chain or weak vaccine management practices, but is a direct consequence of the presentation of a vaccine in multi dose vials.
Maybe the answer to that question can be found by looking at differences in wastage rates between single dose vial vaccines and multi dose vial vaccines. A study by Parmar et al (
http://www.ncbi.nlm.nih.gov/pubmed/20009517/) looked at reported wastage rates in 19 GAVI countries and found 5% median (total) wastage rate for single dose vials and 10% for 10-dose vials. The 10% is questionable, in my opinion, but the 5% may be reasonable estimate for closed-vial wastage? There are several caveats:
- Administered doses may be over-reported, which would make actual wastage higher
- The study only used the 19 countries that were able to report wastage, out of 72 GAVI countries. That may have introduced a bias as these countries may have better systems and management in the first place,
- Some kinds of wastage (especially freezing) may go undetected, and end up being administered.
All of these would push actual wastage rates up, so in conclusion, 5% closed-vial (avoidable) wastage may be a lower limit.
Jan