Enter a clue or pattern or both:
Swollen glands cause (5 letter answer)
The answer MUMPS is rarely seen, appearing only about once every 2100 puzzles.
Kind of vaccine
Common childhood illness, once
Doctors call it parotitis
MUMPS as a noun:
1. (mumps, epidemic parotitis) = an acute contagious viral disease characterized by fever and by swelling of the parotid glands