Understand that both Td and Tdap are adult vaccines and that Td is essentially a booster and Tdap also has protection for pertussis. What happens if someone is given the Td, but not the Tdap? Should they be given the Tdap at a later date upon recognition? Is there another vaccine that can fill the gap in protection? See related question that doesn't really answer my question (or if it does, I don't understand it): On Td/Tdap Vaccine requirement
According to the United States CDC, adults who have not received a dose containing acellular pertussis on or after their 19th birthday should receive a Tdap dose as soon as possible.
Here is an excerpt from the adult vaccine schedule:
Here is a quote from the recommendations:
ACIP recommends that for pertussis vaccination, when indicated, Tdap should be administered regardless of interval since the last tetanus or diphtheria toxoid–containing vaccine. ACIP concluded that, while longer intervals between Td and Tdap vaccination could decrease the occurrence of local reactions, the benefits of protection against pertussis outweigh the potential risk for adverse events.
In the US, there is no preparation which contains only acellular pertussis, as can be seen on the list of approved vaccines. Thus, Tdap is the only option.