# 5.4  Estimating vaccine needs based on the size of immunization sessions

Now we show you how to calculate vaccine needs based on the size of immunization sessions. This method is appropriate if you cannot determine the rates of vaccine wastage, or vaccine stock management is not good. The equation you should use to estimate the annual vaccine needs by this method is given below:

Annual vaccine needs = posts x weeks x sessions x vials x doses, where:

• posts = number of immunization sites
• weeks = number of weeks the service is delivered during the year
• sessions = number of immunization sessions per week
• vials = number of vials opened per immunization session
• doses = number of doses per vial.

Table 5.4 shows how to calculate vaccine needs based on the size of immunization sessions in an imaginary example, using a vaccine supplied in multi-dose vials containing 10 doses per vial.

Table 5.4  Calculation of annual vaccine needs based on the size of immunization sessions.
immunization postsweeks deliveredsessions per weekvials per sessiondoses per vialtotal doses
1x48x2x1x10=960

So the vaccine needs for this particular multi-dose vaccine, based on the size and number of vaccination sessions = 960 doses per year.

• Why do you think an estimate based on the size of the immunization sessions is likely to be higher than one based on previous consumption?

• An estimate based on the size of the immunization sessions assumes that all of the scheduled immunization sessions will actually be held for each of the scheduled weeks in the year. But if some sessions cannot be held (for example, if there was a shortage of vaccine, or if the health worker was ill), then the actual number of vaccine doses given would be lower than estimated using the method illustrated in Table 5.4.

5.3.1  Calculating annual vaccine needs from previous consumption

5.5  Ordering vaccines