However, their integration into routine use at field level has been slower than expected. In spite of the availability of good training materials at the outset, countries were surprised by the arrival of VVMs and few national training plans extended to districts and health unit staff. Field experience has therefore been monitored and reported only since the start of 1997, which has reduced the quantity of data that can now be presented. However, it is an indication of the value of the VVM that the experience gained so far already weighs heavily in favour of the continued use of VVMs for polio vaccine. With the arrival of reliable and accurate impact data, distrust in VVMs has largely evaporated and a strong foundation now exists for using VVMs for all remaining vaccines.
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Vaccine consumption levels and costs could be reduced if a greater proportion of the contents of vials was used. Until 1996, it was recommended that each vial vaccine be discarded at the end of an immunization session. EPI has now settled a new policy which allows for opened vials of selected vaccines to be used for longer. Sufficient data have been collected on the safety and potency of EPI-recommended vaccines to endorse a change in the global policy on the use of opened vials of vaccine. The revised policy could help to reduce vaccine wastage and save money.