As the polio wave eased, Dr. Katz arranged a meeting with John Enders, who shared the 1954 Nobel Prize in Medicine for work isolating strains of the polio virus. For Dr. Katz, it would begin more than a decade of collaboration as a key member of a team that developed a vaccine for measles, a highly contagious virus once common among children that had been blamed for up to 2.6 million deaths a year around the world, including hundreds in the United States.

“I came along at the right time, in the right laboratory, with the right colleagues,” said Dr. Katz, who died Oct. 31 at 95 at his home in Chapel Hill, N.C.

The vaccine was one of the landmark discoveries in childhood medicine during decades that also tamed chronic threats such as polio, rubella and mumps. Dr. Katz then went on to a prominent career in virology and pediatrics that spanned health crises such as AIDS and the covid pandemic and the rise of anti-vaccine movements.

“People have lost sight of what it is they are being protected from,” said Dr. Katz, who was emeritus professor at Duke University after more than two decades as head of its medical school’s pediatrics department.

The World Health Organization estimated the measles vaccine saved an estimated 17.1 million lives between 2000 and 2015 alone. (The WHO reported more than 17,000 measles cases worldwide in January and February this year, compared to 9,665 during the first two months of last year. The Centers for Disease Control noted 33 measles cases in the United States so far this year.)

When Dr. Katz arrived at Enders’s lab in Boston, the measles virus had already been isolated from a local schoolboy, David Edmonston. The challenge was to find a way to make an “attenuated,” or weakened, virus that could be the foundation for a vaccine.

“And indeed we went to embryonated hens’ eggs,” Dr. Katz said in a 2014 interview for the podcast “Open Forum Infectious Diseases.”

The “Edmonston virus” was passed through chick embryos more than a dozen times, reducing its strength. It was then injected in monkeys by the Enders-led team, which included a research fellow from Yugoslavia, Milan Milovanovic. The monkeys developed none of the classic symptoms such as fever and rashes or showed viremia, the presence of the virus in the bloodstream. But the monkeys had antibodies.

“So we were on our way,” said Dr. Katz.

The human trials underscored some of the ethical questions during an era of less-regulated vaccine research, such as flu vaccine tests in the 1940s on children at a Pennsylvania mental-care institution and Albert Sabin using federal prisoners in Chillicothe, Ohio, in late-stage polio vaccine studies in 1954 and 1955.

The Enders team used the Walter E. Fernald State School in Waltham, Mass., a facility for children with severe neurological disorders. Dr. Katz said about 20 patients were picked and parental consent was given.

“We injected these youngsters with the chick cell virus and observed them daily,” Dr. Katz said in the podcast. “We did throat cultures. We did blood cultures. And they never had any viremia, they never had any virus in their throat. … So we had made the big jump.”

The findings were published in 1961 in the New England Journal. Inquires started to flood in.

Those included letters and telegrams from a British pediatrician, David Morely, in Nigeria. He appealed to expand the measles vaccine tests to Nigeria, where the mortality rate for the illness was as high as 15 percent.

The work by Dr. Katz in Nigeria produced important insights for global vaccination efforts, including how infants with measles often stopped breastfeeding because of mouth sores and became severely dehydrated. Simple hydration treatments were added to measles vaccine regimes in Nigeria and elsewhere.

The measles vaccine was licensed in the United States in 1963. (In 1971, it was incorporated into the measles, mumps and rubella, or MMR, vaccine.)

Walter Orenstein, associate director of the Emory University Vaccine Center in Atlanta, said Dr. Katz played a critical role in shaping U.S. public health policies while serving on the CDC’s advisory committee on immunization practices from 1982 to 1993.

“He understood that it’s not the vaccines that save lives, but the vaccinators,” said Orenstein. “A vaccine sitting in a vial unused is zero percent effective.”

Navy medicine

Samuel Lawrence Katz was born May 29, 1927, in Manchester, N.H., where his father began his workday commute to Boston as a railway executive. Dr. Katz started undergraduate studies at Dartmouth College in 1944 but left to enlist in the Navy the following year.

“After going through boot camp, they gave us tests and said, ‘Oh, you’re a bright boy. We’re going to send you to college,’ ” Dr. Katz told a Dartmouth alumni magazine in 2009. “I said, ‘No, no, I just came from college.’ ”

He was assigned to a hospital training school in San Diego. “That was my introduction to medicine,” he said.

He returned to Dartmouth after World War II, graduating in 1948 and entering a two-year preclinical program at Dartmouth’s medical school. Dr. Katz graduated from Harvard Medical School in 1952.

After his work with Enders, Dr. Katz joined the Duke University School of Medicine faculty as head of pediatrics in 1968 and led the department until he stepped down in 1990 to devote more attention to research including ways to better treat HIV and prevent in children.

Dr. Katz’s first marriage, to Betsy Cohan, ended in divorce. His second wife, Catherine Wilfert, a leader in the field of pediatric AIDS, died in 2020 after 49 years of marriage. Survivors include six children from his first marriage, John Katz, Deborah Miora, William Katz, Susan Calderon, Penelope Katz Facher and David L. Katz; two stepchildren, Rachel Wilfert and Katie Regen; and 17 grandchildren. A son from his first marriage, Samuel L. Katz Jr., died in 1980.

David Katz confirmed his father’s death but did not provide a specific cause.

Among Dr. Katz’s many awards was the Albert B. Sabin Gold Medal in 2003.

Over the decades, he wrote commentaries on medical topics, including some that were politically sensitive. He was opposed to having physicians assist with prison executions, and he called for limits on pharmaceutical companies’ ability to hold patents that keep generic drugs off the market.

He also confronted vaccine skeptics and those who are anti-vaccine who cited scientifically debunked claims of side effects such as autism or neurological disorders.

At a hearing before the House Committee on Government Reform in 1999, Dr. Katz recounted a world before many of the modern vaccines.

“Most young parents cannot appreciate, fortunately, as I do, the horror of polio with iron lungs and crutches; measles with encephalitis; meningitis due to haemophilus influenza B … tetanus of newborn infants with overwhelming mortality; and a number of the other infectious diseases that we fortunately do not see,” he testified.

“It is true that despite all that vaccines have done to improve the health of individuals and communities in the United States and throughout the world, they are not perfect,” he added. “However, one simple fact cannot reasonably be disputed — the benefits of immunizations far outweigh any possible risks.”