Evaluating the safety of combination vaccines.

The development of combination vaccines is important to facilitate protection of people from potentially life-threatening infectious diseases. As with all vaccines, the safety of these products is of critical importance. Although combination vaccines generally include components that have been studied and used previously, the possibility of new or more severe reactions arising from combining components cannot be dismissed. Controlled safety studies are needed for new combination vaccines to determine reliably whether risks are increased compared with administration of individual components. Such studies will generally be smaller than studies of vaccines with new immunogens, but the size of the study will depend on the types and rates of the reactions expected, given the vaccine's components, and on the level of increased risk that would be important to detect.