"CDC's current estimate is that Tdap vaccination protects against whooping cough in about 7 out of 10 people who receive it.  According to the California Department of Public Health, the primary DTaP vaccine series is essential for reducing severe disease in young infants and should not be delayed. DTaP can be given to infants at an accelerated schedule with the 1st dose given as early as 6 weeks of age. Even 1 dose of DTaP may offer some protection against severe pertussis disease in infants."  [There is also a current (1/15/15) outbreak in Canada].