Sixteen pupils at a high school in Nottinghamshire are suspected of being hit by swamps.
Public Health England (PHE) said it is investigating a number of reports at Toot Hill School in Bingham.
In a statement, head teacher Sandy Paley said they "work closely" with PHE and advised all parents and staff.
She added: "Our first priority is always the well-being and health of our students and we continue to monitor the situation closely."
The suspected mumps cases come months after hundreds of cases were confirmed among university students in Nottingham and in the midst of a decline nationally in the uptake of child vaccinations.
Vanessa MacGregor, a health protection consultant with PHE, said there has been an increase in suspected cheating cases, with teens and adolescents who have not had two doses of MMR vaccination "particularly at risk".
"Young adults who haven't received MMR or just a dose should make sure they take up the MMR vaccination offer," she said.
"However, it is not only students who are at risk and we urge anyone who has not received two doses of MMR vaccine to do so."
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