A new study is shedding light on the cause of a recent series of whooping cough outbreaks among children who'd already been fully vaccinated against the disease.
Researchers in Marin County, Calif., discovered that the whooping cough vaccine becomes largely ineffective three years after being administered.
"I was disturbed to find maybe we had a little more confidence in the vaccine than it might deserve," lead researcher Dr. David Witt said. Witt is chief of infectious disease at the Kaiser Permanente Medical Center in San Rafael, Calif.
Last year, California saw a massive spike in whooping cough cases. More than 9,100 people became ill and 10 infants died.
"What we identified pretty quickly was that the bulk of the outbreak was in vaccinated, fully vaccinated up-to-date children," Witt said Monday at the American Society for Microbiology conference in Chicago.
Under current federal guidelines, the vaccine is given in five doses. The first shot is administered at two months and the final one between 4 and 6 years of age.
Children are supposed receive a booster shot at around 11 or 12 years old, but the study's findings may cause some to question whether that should be done sooner.
Meanwhile, San Diego County health officials cautioned in a statement that the research was only preliminary.
"This is a preliminary study that has not been fully reviewed by local and state health officials," they said.
"Further, the County does not make recommendations about routine vaccine intervals," they added. "We follow recommendations that come from the CDC's Advisory Committee on Immunization Practices."