Albertus Dominicus Marcellinus Erasmus "Ab" Osterhaus (born 2 June 1948) is a leading Dutch virologist and influenza expert.

An Emeritus Professor of Virology at Erasmus University Rotterdam since 1993, Osterhaus is known throughout the world for his work on SARS and H5N1, the pathogen that causes avian influenza.

He fulfilled several positions in his 16-year career at the Netherlands National Institute for Public Health and the Environment (RIVM) in Bilthoven, the last of which was head of the laboratory for Immunobiology.

In February 2004, his team found that Pegylated interferon alpha [de], a drug used for the treatment of patients with Hepatitis C, helps combat the virus that causes SARS.

During debate 'De Kwestie live' he said "I have named a wide spectrum of possibilities and minister Ab Klink decided to go for the worst-case scenario" [9][10] In September 2009, a controversy arose when it became known Osterhaus has a 9.8% share in ViroClinics B.V, a pharmaceutical company that supposedly benefits from the 34 million vaccines Health minister Ab Klink bought based on his advice as government consultant.