Evaluating the safety of combination vaccines

The development of combination vaccines is important to facilitate protecti on of people from potentially life-threatening infectious diseases. As with all vaccines, the safety of these products is of critical importance. Alth ough combination vaccines generally include components that have been studi ed and used previously, the possibility of new or more severe reactions ari sing from combining components cannot be dismissed. Controlled safety studi es are needed for new combination vaccines to determine reliably whether ri sks are increased compared with administration of individual components. Su ch studies will generally be smaller than studies of vaccines with new immu nogens, 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 in creased risk that would be important to detect.