Later, he went on to work for the Leuven Institute of Bacteriology under the auspices of Professor Richard Bruynooghe. In 1954, he founded the Leuven Rega Institute for Medical Research.
De Somer also helped build the Gasthuisberg Campus of the University Hospital Leuven into the largest hospital in Belgium. In 1968, he became the first rector of KU Leuven, one of Flanders’ five universities, which he remained until his death in 1985.