The target population is the number of people who are eligible for vaccination with a particular vaccine. We use the letters ‘pt’ to represent the target population in calculations.

For tetanus toxoid (TT) vaccine the target population is the total number of pregnant and non-pregnant women in the childbearing age-group (15–49 years). (Children will usually be protected from tetanus by receiving three doses of pentavalent vaccine at 6, 10 and 14 weeks of age.)
For BCG vaccine, the target population is all live births (i.e. complete expulsion from the mother, regardless of duration of pregnancy, showing any evidence of life).
For all other vaccines in the Expanded Programme on Immunization (EPI), the target population is all surviving infants (i.e. survive to their first birthday).

To calculate vaccine needs based on the target population, you need to know the size of the target population, the number of doses required according to the EPI schedule, and the percentage immunization coverage rate you have been given as the target in your annual activity plan.

Annual activity plan performance for immunizations in a community with a total population of 6,348 people in 2003 E.C. (Ethiopian calendar, or 2010 in the European calendar). (Photo: Janet Haresnape)

In the figure the column headed ‘eligible’ gives the number in the target population for each vaccine. You can see that the health professionals in this health facility planned to immunize 100% of the eligible children and 100% of the pregnant women (TT+2 PW, pregnant women receiving more than 2 doses of TT vaccine). Columns headed P refer to ‘planned’ numbers for immunization, and A are the ‘actual’ numbers immunized — in the first quarter of the year, they exceeded their targets for all categories except TT+2 NPW (non-pregnant women of childbearing age receiving more than 2 doses of TT).