The rotavirus and HPV vaccines were contentious subjects and might never have reached the market without Dr. Mahmoud’s determination, said Dr. Julie L. Gerberding, an executive vice president at Merck & Co., and former head of the federal Centers for Disease Control and Prevention. She joined Merck after Dr. Mahmoud retired but described him as a “lifelong mentor.”

Dr. Mahmoud championed those vaccines because he recognized their potential to save lives, she said. Globally, cervical cancer and rotavirus infections kill hundreds of thousands of women and children every year.

The problem with a rotavirus vaccine was that another company had already developed one but then had to take it off the market because it was found to increase the risk of bowel obstruction in infants. Opponents argued that it would take a large study and a huge investment of time and money to test Merck’s candidate vaccine, and then to overcome public fears.

“Everyone wanted to kill it,” Dr. Gerberding said. “Adel said, ‘Not only are we going to do it, but we’re going to make our study even larger to prove it works and is safe.’ ”

Dr. Mahmoud took a similar approach to the HPV vaccine, which also had its detractors. Some doubted that it would work. Others thought parents would reject it, fearing that vaccinating young girls would somehow encourage them to start having sex. That fear was based on the virus’s being sexually transmitted and the view that the vaccine was most effective if given before girls become sexually active.