On the CDC website,
Is HFMD Serious?
HFMD is usually not serious. The illness is typically mild, and nearly all patients recover in 7 to 10 days without medical treatment. Complications are uncommon. Rarely, an infected person can develop viral meningitis (characterized by fever, headache, stiff neck, or back pain) and may need to be hospitalized for a few days. Other rare complications
can include polio-like paralysis or encephalitis (brain inflammation), which can be fatal.