How long is the tdap vaccine effective for?

Depends: When given to a 2 month old with an immature immune system its benefits begin to wain within 3-6 months(which is why they get boosters). If given to a five year old who completed the primary series, you get 5-10 yrs which is about all you can get with the adult preparation in the adult population..

EFFECTIVE 10 YEARS: It is recommended a booster be given every ten years, as first tdap is given at age of 11, to children who have completed primary vaccination ate age four with five doses of dtap, that is three doses in first year, one in second year after age 15 months, fifth at or after age 4 years. Only exception is if there is a dirty cut after 5 years than a booster of tetanus toxoid or combined tdap may be given.