Enhanced toxicity for mice of pertussis vaccines when preserved with Merthiolate.

Pertussis vaccines preserved with 0.01% Merthiolate are more toxic for mice than unpreserved vaccines prepared from the same parent concentrate and containing the same number of organisms. The toxicities of both Merthiolate (0.01%)-preserved and unpreserved vaccines increased when the number of organisms injected was increased. An increase in mortality was observed when Merthiolate was injected separately, before or after an unpreserved saline suspension of pertussis vaccine.