The vaccine for whooping cough grows less effective with time, according to a study published in Pediatrics and cited by CNN.
To conduct the study, researchers at the Kaiser Permanente Vaccine Study Center in Oakland, Calif., analyzed data on 469,982 children born between 1999 and 2016. They found 82 percent of cases occurred in children who were fully vaccinated.
Physicians administer the vaccine, called DTaP, in a series of doses until children turn 11 or 12, including five doses before age 7. The new study found children were more likely to contract whooping cough as more time passed since their final dose. For example, a child who received his or her last vaccine dose more than three years ago was five times more likely to contract whooping cough than a child vaccinated in the past year.
Nicola Klein, PhD, MD, study co-author and director of the Vaccine Study Center, said the vaccine is generally effective, but noted that most children in California's whooping cough outbreaks had been vaccinated.