Bill Gates published a thank you note this week to the coalition of organizations working to eradicate polio. The news: the number of polio cases — 242 in 2014 – has fallen to 51, according to UNICEF. The agency said this week that in no time in history has the number of children who contract the disease been lower.

Gates has set eradicating polio as one of his chief philanthropic objectives, and the Bill and Melinda Gates Foundation spent around $44 million on the disease in 2014, about 23 per cent of the  $1.9 billion the foundation spent for development programmes. Other organizations involved in the Global Polio Eradication Initiative include the World Health Organization, Rotary International, Centers for Disease Control and UNICEF itself. As a part of the initiative, UNICEF delivered 1.7 billion doses of vaccine in 2014 and supported the training of front-line workers in communities from Karachi in Pakistan to Kano state in Nigeria.

For the first time ever, Nigeria has succeeded in interrupting transmission of wild poliovirus, and last month it was removed from the list of polio endemic countries. That means the disease prevails in just two countries: Pakistan and Afghanistan. However, the organization pointed to outbreaks in Laos, Ukraine, Guinea and Madagascar derived from vaccinations, and cautioned that many countries still need to improve their systems of routine vaccination.