Health experts are warning young adults are at risk of developing mumps because many of their age group missed out on getting two doses of the MMR jab as children.
Latest figures show cases of mumps in England have reached their highest level in a decade.
So why is mumps a risk, and how effective is the MMR vaccination?
Is mumps risky for adults?
It can be.
The viral infection used to be very common in children before the MMR jab was introduced in the UK in 1988.
It usually causes painful swelling in the glands at the side of the face, plus joint pains, fever and tiredness.
Most recover without treatment. But it can cause complications including:
Swollen testicles – this affects one in four men who get mumps after