There is now a huge cohort of children who are not protected and this has allowed the measles virus to circulate - often infecting babies who are too young to have had the MMR vaccine.

BBC: Long shadow cast by MMR scare

Twenty years after the global outbreak of AIDS, no one has developed an effective vaccine against the HIV virus, a far more cunning foe than polio, smallpox or measles.

FORBES: Outsmarting AIDS