Following a measles outbreak in Rockland County in New York State, authorities there have declared a state of emergency, with unvaccinated children barred from public spaces, raising important questions about the responsibilities of the state and of individuals when it comes to public health.

Measles virus is spread by people coughing and spluttering on each other. The vaccine, which is highly effective, has been given with mumps and rubella vaccines since the 1970s as part of the MMR injection.