Vaccines have a special role in public health - they are given to healthy children, to prevent serious diseases like hepatitis B, diphtheria, pertussis (whooping cough), and bacterial meningitis. Since the introduction and widespread use of modern vaccines over the last century, hundreds of millions of lives have been saved all over the world. In many countries, diseases such as measles, rubella, and poliomyelitis have been eliminated completely.

Vaccines have become so central to modern public health it would be easy to take them for granted. But vaccines are complex biologic products, requiring strong regulation and management to ensure that they are manufactured properly, and handled correctly at every step from factory door, to clinic, to child. Without careful handling, vaccines can lose some of their potency and effectiveness.

Last week's exposure of a criminal ring re-selling vaccines across China has revealed problems in one part of this supply chain - the distribution of vaccines available for purchase on the private market.