A new study during an outbreak in California in 2010 found immunized children between 8 and 12 were more likely to catch the bacterial disease than kids of other ages.
Scientists say the durability of the vaccine is not what was imagined.
The CDC recommends that at age 11 or 12 children get the booster.
But authors of this study say they believe the booster is too late and leaves pre-teens at an increased risk.
