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From the website: "Those children whose maternal immunity wears off early are at risk of infection at an age when measles infection can be most severe. Thus, health systems in endemic regions, like the DRC, employ a first dose at a relatively early age (nine months) to immunise these vulnerable children. Later they provide a second dose to catch those for whom the first dose didn’t provide protection.
The weak spot of this strategy is the accessibility of routine preventive health services. In the DRC, as in many underfunded health systems, many families cannot routinely access timely preventive services. This can be because they live too far from clinics, or because clinics are in bad shape."