Vaccines are appropriately evaluated for mutagenicity, carcinogenicity and impairment of fertility, when necessary, as a part of pre-clinical or nonclinical studies that occur even before the first phase one studies on people.
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Vaccines are thoroughly tested for both safety and efficacy and they are also tested in the different combinations on the routine childhood immunization schedule.
When it is ethical to do so, placebos have been used in vaccine trials, even saline placebos.
