There is little doubt that global efforts to increase vaccination coverage levels among children in developing countries have been effective at increasing the number of children receiving vaccines as well as the number of children who get sick from these preventable diseases. The most recent and perhaps most dramatic example of such success comes from recent efforts to immunize children against measles in Africa. Measles deaths in Africa decreased by about 90% from 2000-2006 following widespread immunization from the vaccines. Widespread adoption of the measles vaccine is perhaps one of the most notable, and I would argue, most under appreciated successes of global health during the past decade.

However, the experiences of other immunization campaigns are not always as dramatic or as positive as the measles story. More often than not we hear about how immunization coverage rates regularly stagnate at levels below those considered optimal for population-level goals, coverage rates wane in some countries, and child mortality declines have not been as large as we would have hoped. Vaccine preventable diseases remain major killers of children throughout Africa, despite many decades of efforts to immunize children against these diseases.

Two recent research papers published in the Lancet have made me aware of two important challenges to immunization programs that I have not given much thought to in the past. In my own research, I have likely glossed over some of the complexities of immunization programs in an effort to analyze complex situations in a simple way (this is, after all, what economists do).

In the first paper, Andrew Clark and Colin Sanderson discuss how traditional measures of immunization coverage do not adequately measure an important aspect of immunization: timing. Aggregating data from dozens of Demographic and Health surveys, they analyze the timing of immunizations relative to the recommended timing for such vaccines and find significant delays in coverage, in most cases a few weeks for each vaccine, but climbing to a few months for the vaccines requiring multiple dosages. In the lowest performing countries, the delays could be very extreme. They have two main findings, such timing may affect the overall effectiveness of immunization programs, but also suggests problems with the current measures used to calculate coverage levels.

In the second paper, Sara Lowther and co-authors conducted a follow-up survey of children in Lusaka, Zambia three years following a major immunization drive to measure effective coverage of the vaccines (measured in terms of having antibodies against measles). They find that only about 70% of children have these antibodies three years after the campaign, which is explained partly due to the fact that a substantial children never received the vaccine, and that immunization naturally wanes over time. As such, coverage levels were sub-optimal.

Both of these papers highlight important challenges in translating what we know works, in theory, to reality. We need better measures to help assess the timeliness of such programs and better ways to measure the impact of these efforts over time.

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