DTaP/Tdap/Td vaccines – which is which?

There is often confusion between the different vaccines that protect against tetanus, diphtheria and pertussis.  DTaP, Td, and Tdap are all different vaccines, and they are used in different populations, from infancy to older adulthood.

A quick primer on the alphabet:

  • D is for diphtheria – an illness caused by Corynebacterium diphtheriae, the symptoms involve cough and fever and can progress to cause difficulty breathing by what is called a “peudomembrane” developing in the throat.  Most common in children; spread by one who has it coughing in proximity to others who are susceptible.  Occasionally it can be fatal.  Nowadays diphtheria is rare in the U.S.
  • T is for tetanus, also called “lockjaw” by my grandparents, this is a bacterial infection caused by Clostridium tetani.  Most people think of this as a wound infection (for me it brings to mind the “stepping on a rusty nail” image).  Also can contaminate canned foods.  Can cause severe and painful muscle contractions of  most muscle groups.  Go to the ER with a dirty wound, and you’ll commonly leave after a tetanus booster if you are not sure of your last dose.  Uncommonly seen nowadays because the vaccines are so effective against tetanus.
  • P is for pertussis – an under-recognized illness, characterized by a severe or prolonged cough.  In the unvaccinated patient usually there is high fever but in many who have received the vaccine it causes an annoyingly persistent cough that can go on for weeks or more.  Besides a persistent coughing illness in older children, pertussis is well known to infect newborns, and in them it can be very serious, especially in babies under 2 months old, who can develop apnea and respiratory failure and even death.  For this reason women receive an extra dose of a pertussis-containing vaccine with each pregnancy (see below).


DTaP is the vaccine used in infants and children up to 6 years old.  Vaccination starts at 2 months old, and is normally given at 2, 4, and 6 months of age, with a booster dose at age 4-6 years.  For the very young, pertussis (the “P”) is a key part of the protection, as pertussis can be life-threatening in newborns.  The prior version of this vaccine, called DTP (no “a” for “acellular” pertussis) was very effective but caused a lot of high fevers and behavioral changes and was phased out starting in 1998.

Tdap is the version given at age 11 years; only once (for now) unless you are a woman and become pregnant – then you get an additional with each pregnancy (see above).  Protection lasts 10 years against tetanus BUT we know that the pertussis protection wears off much earlier.  Someday this is likely to be replaced by a more effective version that gives more pertussis immunity. 

Td (tetanus and diphtheria components only) is the version that adults get every 10 years, or after 5 years with a “dirty wound”.  May be replaced by Tdap in the future if a more effective version of it gets approved.


Infants and young Children receive DTaP:

  • 2 months old
  • 4 months old
  • 6 months old
  • 12-15 months old
  • 4-6 years old


Preteens receive Tdap:

  • 11 years old (once only)


Pregnant women receive Tdap:

  • in the 3rd trimester of EACH pregnancy


Everyone else who has received one dose of Tdap already receive Td:

  • every 10 years for life

Author: marcgrella

Primary care pediatrician; vaccine advocate; hunger fighter; refugee supporter.

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