The infant will develop artificially acquired active immunity
medicine containing dead or weakened pathogens
You are giving the definition of a vaccine but not "what is the following to choose from"
A weakened or modified virus that is introduced into an organism to stimulate immunity is called a vaccine.
a vaccine
Because they have either respectively not yet developed sufficient immunity, or may have weakened immunity.
That is called a vaccination.
Immunological memory, which is the name for when the "adaptive immune system" remembers the weakened or dead foreign molecules and uses that memory to destroy them far earlier when the real disease comes about.
it will reduce the immunity
Vaccine
Vaccine.
immunity is protection from a bacteria and it can be obtained by introducing a dead/weakened version of that organism into the blood stream or muscles, i.e. a vaccine
Its called a Vaccine