there is no medical "immunity" to pills. but your question is about birth control, and this has a very wide scope, including natural family planning
, calendar method, tubal (fallopian tube
) ligation, condoms, etc. and although strictly speaking, there is no immunity, these methods of birth control each have their own failure rates.
if your method of birth control fails and you conceive a child, this is not due to immunity but to other factors (depending on which method you are using) that may lead to method failure. :)