Put simply, the more people we vaccinate the less per person it costs us to deliver the service and we pass those savings onto our clients.  

The proposal we send you for your flu vaccination program is an estimate with the final cost being calculated from the services we deliver on the day.  So, if the number of vaccines we administer is more or less than you estimated, we will charge for the service we deliver not what was estimated.  This has the advantage that you will not be charged for vaccines we do not administer and we will invoice you at the price per vaccine that reflects the number of vaccines administered, not the number that was estimated.