His role in the World Health Organisation is to make sure the smallpox vaccines are safe and effective, wherever they are used in the world.
Elwyn Griffiths: 
Diseases don't respect national borders. As a microbiologist at the World Health Organisation, I'm responsible for the quality and safety of all biological medicines ("biologicals") including polio and meningitis vaccines.
My team of 12 in Geneva works closely with the top biologicals specialists world-wide - just 50 people - developing and establishing international guidelines for vaccines, blood products and cutting-edge gene therapy products.
At the moment the big push is to find ways to eradicate malaria, TB and HIV, and to achieve global agreement on what needs to be done in gene therapy clinical trials to ensure the health of the whole human population is not damaged.
Science is about the thrill of discovering what's new and understanding nature. Working for an international organisation, such as the WHO, gives you the opportunity to work with great minds from all over the world. Science is hard work, but it has tremendous rewards at the end of the day. I find it fascinating. 
The Science
All biologicals are either extracted from biological material like blood, made by bacteria, or grown in culture from human and animal cells. Sometimes biologicals consist of the live organisms themselves. The trick is to keep the biologicals safe yet effective. This is key whether they are vaccines, blood products, or gene therapy products.
The WHO doesn't develop biological medicines. Its role is to write recommendations, after international consultation with specialists, detailing how biologicals should be made, with benchmarks for quality and safety. The WHO's recommendations aren't legally binding, but they're very influential, becoming the international standard as countries adopt them or use the guidelines as the basis for their own regulations.
As well as these written standards, WHO sets the physical standards that scifiles use for measuring the activity of biologicals. For instance, WHO labs in London and Amsterdam distribute vials of biological medicines to individual countries so that their national standard can be calibrated against the WHO standard. This then forms the basis for clinical dosing or the specification for a vaccine. WHO cannot dictate; all countries are part of the standard-setting process.
