The introduction of routine immunisation with pneumococcal conjugate vaccines (PCVs) in developing countries is expected to significantly reduce childhood deaths 
. The 7-valent pneumococcal conjugate vaccine (PCV-7), containing serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F, is highly efficacious against invasive pneumococcal disease (IPD) of vaccine serotype, plus serotype 6A 
. Routine immunisation with PCV-7 has led to dramatic decreases in IPD due to pneumococci of vaccine serotype, but variable increases in IPD due to pneumococci of non-vaccine serotype 
. Therefore, it is essential to monitor the introduction of PCVs in different settings. Demonstrating the impact of PCVs will be crucial for ongoing immunisation policy.
In 2009, the Government of The Gambia introduced routine PCV-7 vaccination into the national Expanded Programme of Immunisation (EPI) with support from the GAVI Alliance. Three doses of PCV-7 are given at 2, 3, and 4 months of age. A limited catch-up campaign gave at least two doses of vaccine to approximately 50% of children aged 2–11 months and one dose of vaccine to approximately 10% of children aged 12–23 months. PCV-13 replaced PCV-7 in April 2011 without a catch-up campaign.
The importance of pneumococcal disease in The Gambia was indicated by a 16% reduction in all-cause mortality in children 2–29 months of age in a trial of PCV-9 conducted in Upper and Central River Regions 
. There was a 71% reduction in IPD of vaccine serotype and a 35% reduction in radiological pneumonia. The incidence of IPD and radiological pneumonia in the placebo arm was 390 per 100,000 person years and 37 per 1,000 person years, respectively. The incidence of IPD in this part of The Gambia was estimated previously to be 554 and 240 per 100,000 person years in under 1 and under 5 year-old children, respectively 
. Neither the burden of IPD, nor the extent of the indirect (herd) effect of PCVs, are known in older children and adults in The Gambia, although PCV-7 vaccination of Gambian infants has recently been shown to reduce carriage of vaccine serotypes in older subjects 
Serotype coverage of IPD in The Gambia with PCV-7 and PCV-13 is approximately 30% and 70%, respectively 
. Consequently, there is a large reservoir of pneumococci of non-vaccine serotypes available for replacement 
. We developed a surveillance system to monitor the incidence of vaccine and non-vaccine type IPD and radiological pneumonia in those aged 2 months and older, before and after the introduction of PCVs. The data, when available, will provide key information to support PCV immunisation policy in The Gambia and elsewhere in Africa. Here we describe how this surveillance system was set up and is being operated.