Frozen DTaP vax has unintended effect

Inadvertent freezing of the DTaP (diphtheria, tetanus, and acellular pertussis) vaccine during storage may be contributing to a rise in one of the diseases it aims to prevent. The unlikely culprit: well-meaning nurses.

Investigators from Baylor College of Medicine in Houston wanted to know why pertussis was on the rise in the nine years following the vaccine's debut. The disease had been in decline for ten years after DTaP's predecessor, the DTP vaccine, went to work.

Using continuous data loggers, researchers found that a quarter of the 54 vaccine refrigerators in community health centers showed temperatures that dipped below freezing. The dips occurred at night and on weekends.

During interviews with staff, researchers found that conscientious nurses often detected warmth when they opened the refrigerator doors during the workday. So they adjusted the temperature downward. "They were freezing the vaccines like crazy," says Patrick McColloster, an associate professor of family medicine at Baylor, in Internal Medicine News.

DTaP uses aluminum as an adjuvant, he explains. DTP does, too, but the aluminum in DTaP is more sensitive to freezing, he explains.

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