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From John Grange

Vaccines influence the immune system in more ways than Michael Brooks describes (17 August, p 38). They can give a useful degree of protection against certain cancers. Studies in several countries have demonstrated that the tuberculosis vaccine BCG, when given early in life, confers some protection against acute leukaemia .

There is also evidence that BCG or smallpox vaccination early in life reduces the subsequent risk of melanoma, an aggressive skin cancer, by around half. Moreover, vaccinated people who do develop melanoma have a better prognosis than their unvaccinated counterparts ().

Preliminary evidence indicates that yellow fever vaccine given to adults also gives some protection against melanoma ().

We need to do more studies to determine the full spectrum of health-enhancing effects of vaccination strategies.
London, UK