A contraindication is a condition in a recipient that increases the risk for a serious adverse reaction to vaccination and is a condition under which vaccines should not be administered. In addition to contraindications found in prescribing information, ACIP may recommend against the use of a vaccine under certain conditions (e.g., a lack of data).
A precaution is a condition in a recipient that might increase the risk for a serious adverse reaction, might cause diagnostic confusion, or might compromise the ability of the vaccine to produce immunity. For example, not vaccinating a person who is moderately or severely acutely ill avoids diagnostic confusion between the underlying illness and side effects of vaccination. Vaccination may be deferred if a precaution is present, although a vaccination might be indicated in the presence of a precaution if the benefit of protection from the vaccine outweighs the risk for an adverse reaction.