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.

The global incidence of measles fell markedly once the vaccine became widely available. But measles control was set back considerably by the work of Andrew Wakefield, which attempted to link the MMR vaccine to autism.

There is no such link, and Wakefield was later struck off by the General Medical Council for his fraudulent work. But damage was done and has proved hard to reverse.