Preben Christian Alexander von Magnus (25 February 1912 – 9 August 1973) was a Danish virologist who is known for his research on influenza, polio vaccination and monkeypox.

He represented Denmark at the 1959 Pugwash Conferences on Science and World Affairs where he explained that respiratory viruses such as influenza and the common cold were unsuitable as biological weapons.

He served on the Danish hospital ship MS Jutlandia and he became a member of the Advisory Panel on Virus Disease of the World Health Organization.

Von Magnus and his wife Herdis were not only Salk's lifelong friends, but were also appointed by the Danish government to direct the vaccination of all 7 to 12 year olds.

[12] The Statens Serum Institut produced its own modified polio vaccine using techniques based on what the von Magnus's had learnt in the spring of 1953, when they accepted an invitation to visit Salk's laboratory.

[13][14] Due to the limited supply of inactivated virus, the Danish institute administered the vaccine subcutaneously, requiring smaller doses.

[15][16] In 1968, the WHO reported that it was not infrequent to observe outbreaks of suspected smallpox and monkeypox in laboratory monkeys at more than twenty-five biological institutions around the world and that further research was warranted to assess susceptibity in humans.

[18] He was a member of the Akademiet for de Tekniske Videnskaber from 1960, of the Royal Danish Academy of Sciences and Letters from 1968, and became Knight of the Order of the Dannebrog in 1965.