A patient receives rabies vaccine injection at Hangzhou hospital, March 22. [Photo/Agencies]

The issue is what happens once the vaccines leave the factory. The government-distributed, free (EPI) vaccines are distributed through a tightly managed, cold chain system.

A WHO-UNICEF evaluation of the EPI management system in 2014 and 2015 concluded that capacity to effectively manage vaccines is very strong.

The problem that last week's events have brought to light, is that distribution of vaccines for the private market do not follow the same high standards.

And sadly, this weakness in the system has been exploited by an unscrupulous few intent on making some quick cash, without any apparent regard for the implications for children's health.

China's EPI system is one of the best in the world.

The results speak for themselves: over 99% of Chinese children are now free for life from chronic hepatitis B as a result of use of hepatitis B vaccination. Poliomyelitis was eliminated 16 years ago. The incidence of measles is 99% lower than during the pre-vaccine era.

These accomplishments should inspire confidence.

Vaccines available for private purchase are also important for children's health.

In fact, there are some vaccines currently only available on the private market in China, which WHO recommends be included in the national immunization program – including for pneumonia/meningitis, pneumococcal, and rotavirus.

This would ensure that all children in China would benefit from the use of these vaccines, and have the benefit of bringing them into the more tightly managed government distribution system.

The ongoing investigation by health authorities and the police into China's vaccine reselling ring shows how seriously the Chinese government is taking this incident.

WHO is in close contact with the health authorities as they conduct their investigation, and have offered our full support.