Koech was instrumental in advancing global understanding of HIV/AIDS and other tropical diseases during the 1980s and 1990s. His groundbreaking work earned him a nomination for Genius Laureate by the American Biographical Institute in 2006.

At 28, Koech co-founded the Kenya Medical Research Institute (KEMRI) with Prof. Mutuma Mugambi in 1979, becoming its youngest director. He led KEMRI for nearly 25 years, establishing it as a global leader in research, particularly in the fight against HIV/AIDS.