Establishing causation will require freezing the vaccine and then testing its immunogenicity in animals, or assessing pertussis immune status in patients who have received vaccines from refrigerators experiencing freezing, he acknowledged.
To address the problem, there are several possible solutions, according to Dr. McColloster. DTaP vaccine vials could be affixed with temperature-sensitive labels that show immediately if they have been frozen. Also, clinics could use refrigerators that do not permit staff to manually adjust the temperature.