Dr. Samuel L. Katz, a virologist who was part of the research team at Harvard Medical School that developed the measles vaccine, an advance more than half a century ago that has saved countless lives, died on Oct. 31 at his home in Chapel Hill, NC. He was 95.

Dr. Katz took up the fight against measles in 1956, when he joined a laboratory at Children’s Hospital Medical Center, now Boston Children’s Hospital. Measles was a major medical threat at the time. In the decade before the vaccine was made available in 1963, nearly every child in the United States had measles by age 15, with three to four million people infected by it every year, leading to an estimated 400 to 500 deaths annually, according to the Center for Disease Control and Prevention. Worldwide, measles killed 2.6 million people a year before the availability of vaccines, the World Health Organization said.

Dr. Katz brought a prototype vaccine to Nigeria in 1961 to immunize children who were highly susceptible to measles because their systems had been weakened by malaria, intestinal worms, vitamin A. deficiency and protein depletion. He vaccinated children in a village there, and they developed immunity.

The measles vaccine was licensed in 1963 and soon became widely available; eight years later, it was incorporated into the combined measles, mumps and rubella vaccine.

Dr. Katz chaired the CDC’s advisory committee on immunization practices from 1985 to 1993. He received the 2003 Albert B. Sabin Gold Medal, which is given to public. Health leaders who save lives through vaccines.