Question about different number of doses and age

[swissmom]

Does anybody know the (medical?) reasoning why kids need fewer doses of certain vaxes if they are on a delayed schedule? The CDC states for example for DTaP:

The fifth dose is not necessary if the fourth dose was administered at age 4 years or older.

Does a more mature immune system produce more antibodies? I didn't find an explanation yet.

[swissmom]

Anybody? Nobody?

[Sileree]

Hmm, yeah that is interesting. I don't have an answer, though. Maybe because older kids get worse reactions?

[alegna]

I *think* that in most cases it's a matter of it "taking" better when the kids are older.

-Angela

[DocJenn]

I asked a drug rep that question about a year ago. He said he'd find out for me. Haven't seen him since!

[mamakay]

Sometimes the earlier doses are there to protect them at a younger age, and the later doses to protect them at a later age. The later DTaP doses were put into place because of waning immunity, primarily.

Then with Hib, the recommendations were made at a time when most kids were colonized during the first year of life naturally, so the vaccine when given later would "build" upon some degree of natural immunity (I think). Also, sometimes the third and 4th doses are generally superfluous, and there only to "catch" the 2% of kids that didn't seroconvert with the first few doses.