noun
negative reaction; unsuccessful vaccination
Medical term for an adverse reaction to a vaccine or an unsuccessful vaccination. Used in clinical and public health contexts.
ワクチン接種後に不善感が報告された。
A negative reaction was reported after the vaccination.
不善感の発生率は非常に低い。
The incidence of unsuccessful vaccination is very low.
Compound of 不 (negative prefix) + 善 (good, successful) + 感 (feeling, reaction). The exact historical derivation is uncertain; the term is used in modern medical Japanese.