Claus Nielsen, MSc, PhD, is Director of Virology, at Statens Serum Institut, Copenhagen, Denmark. Dr Nielsen received his degree from the Faculty of Science, University of Copenhagen, Denmark in 1988, and received a PhD degree from at the Faculty of medicine at the same University in 1993. Dr Nielsen has been a research scientist, senior research scientist and from 1994 to 2004 head of the Retrovirus laboratory (BL-3) at Statens Serum Institut. Dr Nielsen collaborates with of numerous research groups and professional societies. Dr Nielsen is a reviewer for several scientific journals, and author of numerous publications in international journals.