We present the results of 24 population-based measles vaccination coverage surveys conducted in between 2005 and 2011 in 28 locations in Sub-Saharan Africa. In 2008, the WHO African Region measles technical advisory group recommended establishing a measles pre-elimination goal, to be achieved by the end of 2012, with the following immunization targets: >90% national MCV routine coverage, with at least 80% coverage in all districts; and ≥95% SIA coverage in all districts . Routine vaccination coverage reached high levels in several districts of Malawi and in Kirundu (Burundi), but most of the surveys showed insufficient EPI coverage.
Survey results showed that the highest vaccination coverage was obtained through ORI. For most infants 6 to 8 months of age, ORI provided the first MCV vaccination. These infants are at higher risk of complications and death in case of illness highlighting the effectiveness of vaccinating this population in ORI.
EPI coverage appeared to be lower among children aged 9 to 11 months than 12 to 23 months old. This might show a delay in the age of routine vaccination. The recommendation to enlarge the targeted age group for routine activities  should be encouraged and reinforced. This would allow the protection of children that missed the routine age window and slow the build-up of susceptible children contributing to the risk of an epidemic in areas with circulating virus. While EPI programs should be flexible to ensure vaccination, efforts are needed to ensure an early first dose administration as a first priority.
In contexts where SIAs were implemented, coverage was low and far under the targeted 95%. Moreover, in many locations these activities were not implemented or often implemented late, without respecting the recommended interval between SIAs. For instance, in Katanga province, after the 2007 SIA few measles cases were reported. The next SIA was planned in 2010, but this was postponed  contributing to the causes of a large outbreak in 2010-2011 .
Often administrative coverage was higher than survey results. This was most significant for SIA, where all administrative estimates were higher than surveys results. Administrative estimates are often at national level and do not account for provincial or district differences. Population-based surveys can provide specific information on coverage and help target interventions. A model that considers both administrative and survey data has even been developed to characterize the performance of the activities leading to the estimated coverage and help to predict the effect of future vaccination activities . This kind of exercise is very important to adequately assess the risk of outbreaks.
Despite several opportunities, a non-negligible proportion of children remained unvaccinated or had not received the recommended 2 doses. Conversely, for some children ORI provided the third or higher dose. Moreover, children not reached either by EPI program or by SIA were also less reached by ORI. These results highlight that children are not equally reached by vaccination activities and multiplying vaccine opportunities does not always imply that unvaccinated children are reached. Further work is needed to ensure that immunization activities reach unprotected children. And in case of limited resources, previous MCV vaccination activities and their coverage should be evaluated to better allocate resources and improve coverage.
These survey data are subject to limitations. First, surveys were conducted only in settings were measles control strategies were not efficient enough to avoid an outbreak, but where surveillance system detected an increase in measles cases. Vaccine coverage in these areas is likely to be different from places where no outbreak occurred or was detected during the last decade.
Second, although card confirmation is the preferred method for ascertaining coverage, this is not always possible and oral history is considered. For example, none of the children could show a vaccination card for SIA, and only an average of 16.9% of the children considered as vaccinated through EPI could show their vaccination card [range 1.8% - 36.2%]. Vaccination status regarding ORI was better documented as half of the children considered as vaccinated could show their vaccination card [range: 0.0% - 83.4%]. This proportion was generally high, except in Malawi and Maroua where quasi none of the vaccination status was confirmed by card. As a result, over-reporting or under-reporting of vaccination might have occurred, depending on the context and despite probing questions. However, previous studies in areas of high measles incidence have shown parental recall to be reliable .
Third, most of the surveys were conducted within a month after the end of ORIs. There is therefore low risk of recall bias for ORI coverage estimates, especially as there is less risk of card loss. Information on routine vaccination was collected for all age groups, i.e. for children up to 15 years of age. Recall bias, especially for older children for which vaccination in routine vaccination occurred long ago, might be expected. We therefore chose not to present EPI coverage for older age group but this likely resulted in an overestimation of the number of doses received in older age groups.
Finally, although standardized protocols and training of all surveyors was rigorously implemented across settings, there may be additional inaccuracies in the data related to individual interviewers and supervisors as well as the inaccuracies of population data used to select the samples.
It is also important to recognize that although population surveys are a rapid means to obtain a vaccine coverage estimate, without serological confirmation, estimates of coverage remain an inference.