The World Health Organization defines public health as 'the art and science of preventing disease, prolonging life and promoting health through the organized efforts of society'. A) Explain why public health can be regarded as a public good. B) Vaccines are one way to deal with the spread of disease; the success of vaccination programs depends on a significant proportion of the population being vaccinated. Despite this, some of the population choose not to be vaccinated. How would economists explain this behaviour? Explain the welfare implications of such behaviour, and suggest a way the government could intervene in the market for vaccinations to achieve a more efficient outcome.