1 Aug

Patients may ask about a widely reported study suggesting that the pertussis vaccine loses its effectiveness as early as 3 years after the last shot of the five-dose series. The study was presented at the American Society for Microbiology meeting earlier this week.

Researchers studied some 15,000 children in California, including 132 who developed pertussis in 2010, according to the Associated Press. They found that the risk for pertussis was up to 20-fold higher in children who’d received their last dose of vaccine at least 3 years previously compared with those who’d been vaccinated more recently. Children aged 8 to 12 years were at greatest risk. (The last of the 5 shots is usually given between ages 4 and 6, with a booster dose around age 11 or 12).

More than four-fifths of infected children had been vaccinated fully.

The AP reports that CDC officials “acknowledged that the vaccine’s protection declines, but they said the agency’s own studies show the drop-off is not as pronounced” as that observed here.