The tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine given to preteens loses a large measure of effectiveness within a few years, new research reveals. The study findings are published online May 4 in Pediatrics.

Overall, Tdap effectiveness for 1,700 teens born between 1993 and 2000 was pegged at about 64%, but that plummeted to 34% two to four years post-inoculation, the investigators found.