Administration of the combined vaccine instead of separate vaccines decreases the risk of children catching the disease while waiting for full immunisation coverage.  The combined vaccine's two injections results in less pain and distress to the child than the six injections required by separate vaccines, and the extra clinic visits required by separate vaccinations increases the likelihood of some being delayed or missed altogether;   vaccination uptake significantly increased in the UK when MMR was introduced in 1988.  Health professionals have heavily criticized media coverage of the controversy for triggering a decline in vaccination rates.  There is no scientific basis for preferring separate vaccines, or for using any particular interval between separate vaccines. 
This should be the easiest section to write, but many students misunderstand the purpose. The objective is to document all specialized materials and general procedures, so that another individual may use some or all of the methods in another study or judge the scientific merit of your work. It is not to be a step by step description of everything you did, nor is a methods section a set of instructions. In particular, it is not supposed to tell a story. By the way, your notebook should contain all of the information that you need for this section.