Figure 3.

Susceptible population younger than 5 years by vaccination delivery strategy (2000–20)

Estimated total numbers of susceptible people younger than 5 years under different vaccination delivery strategies compared with the size of birth cohort. For countries that have not yet introduced MCV2 (ie, Uganda, DR Congo, and Somalia), there are overlapping trends for incidence rates for the delivery strategies of MCV1 and MCV2 (blue lines) and MCV1 only (green lines) and the delivery strategies of MCV1, MCV2, and SIAs (purple lines) and MCV1 and SIAs (red lines). Overlapping trends are also seen in most analysed years in countries that introduced MCV2 in 2017 or later (ie, Nigeria, Ethiopia, and Madagascar). In Indonesia, the fluctuations seen in the no vaccination strategy are the result of dynamic sizes of the susceptible population affected by natural seasonality of measles transmission. MCV1=the first routine dose of measles-containing vaccine. MCV2=the second routine dose of measles-containing vaccine. SIA=supplementary immunisation activity.