5.5.2 Calculating the minimum stock level
The time between the date of ordering vaccines and the date when you collect them may not be as soon as you would wish it to be. There may be an increase in vaccine demand that you want to respond to quickly, but you may find there are unexpected delays in restocking. Therefore, you should always aim to keep a minimum amount of vaccine in stock. The minimum stock level is the minimum number of vaccine doses that should be in the refrigerator when the next supply of vaccines is collected. Usually, the minimum stock is taken as 25% of the total vaccine needs for the supply period.
The minimum stock level can be calculated using the following equation:
- smini = qperiod x 25% (or 0.25)
where smini is the minimum stock level and qperiod is the vaccine needs for the period.
Imagine that at a particular Health Post, the number of doses of oral polio vaccine (OPV) required for a 2 week supply period is 80. If the minimum stock should be 25% of the total vaccine needs for the supply period, what should the minimum stock level be at this Health Post when the next supply of vaccine is collected from the health centre? (Remember that 25% is expressed as 0.25 in calculations.)
The number of doses of OPV required for 2 weeks is 80.
The percentage required as minimum stock is 25% (0.25).
So the minimum stock is 80 x 0.25 doses, or 20 doses.
This means that there should be at least 20 doses of OPV in stock at this Health Post when the next supply of vaccine is collected.