Parents in Bristol are being urged to check their children are up to date with their vaccinations.
NHS England says hundreds of children in the city are not protected against diseases including meningitis, diphtheria and measles.
NHS England South says they have at least 90% coverage in the local population as a minimum target to prevent infections spreading.
NHS England says it is not too late for children to catch up with their vaccinations, ensuring that they are fully protected. Parents and carers are urged to speak to their GP surgery.