Even at age 83, the challenge remains everything to Dr. James D. Cherry. Whether in his career as a scientist researching pediatric infectious diseases or as an outdoorsman who routinely shuns groomed runs to instead hike up snow-covered peaks to ski remote backcountry slopes, “the challenge is what interests me,” he says.

Dr. Cherry, UCLA Distinguished Research Professor of Pediatric Infectious Diseases, is a world expert on bordatella pertussis, the bacterium that causes whooping cough. And he is a fierce advocate for sometimes unpopular but, in his view, essential evidence-based immunization strategies against the illness. His dual passions for medicine and skiing have intersected in small but satisfying ways over the years. He has presented more than 220 lectures around the world on vaccine-preventable disease, affording him opportunities to ski throughout the United States, Canada, Chile, Argentina, France, Austria, Switzerland and New Zealand.

With a lean, still-athletic physique and a serious but soft-spoken demeanor, Dr. Cherry continues to demonstrate a ferociously adventurous spirit. Now in semi-retirement, he continues to co-edit the iconic "Feigin and Cherry’s Textbook of Pediatric Infectious Diseases" — the seventh edition of the two-volume text was just released. He is currently working on several statewide studies of pertussis infant deaths and the use of exchange blood transfusions to treat severe pertussis in infants. He also returned this winter from an annual backcountry ski trip along the border of Chile and Argentina.

Skiing is a passion that began early in Dr. Cherry’s life. He received his first pair of skis as a Christmas gift when he was 4 years old, in 1934. Chair lifts didn’t exist then, and only one ski area in the country had a rope tow, so the New Jersey boy learned to trudge uphill while carrying his Sears & Roebuck skis — a pair of wooden planks with leather toe straps. Perhaps it was that early determination that set Dr. Cherry on his path. He excelled at sports throughout his childhood: track, basketball, soccer and, of course, skiing. While a student at the University of Vermont College of Medicine, he worked holidays as a member of the Stowe Ski Patrol. He continued to ski while pursuing his residency and fellowship in pediatrics and infectious disease at Boston City Hospital and Kings County Hospital Center and during breaks while earning his M.Sc. degree in epidemiology from the London School of Hygiene and Tropical Medicine.

Now a little stooped and slowed by three compression fractures in his back, Dr. Cherry still gets on the slopes as many as 40 days a year. He regularly stretches and recently took up yoga to keep in shape. In 2008, he earned Level One avalanche certification and now carries a shovel, a probe and a beacon, among other supplies, in case a member of his skiing group is caught in an avalanche and has to be rescued. Not even that potential danger can dissuade him from heading to the backcountry. “I like getting off the trail and going through trees,” he says. “The sense of freedom it gives is thrilling.”

Not all of Dr. Cherry’s survival tools are of the physical sort that would fit into a backpack. With more than 50 years of experience in research, teaching and clinical practice in pediatric infectious diseases and epidemiology, Dr. Cherry has played a major role in shaping vaccination strategies against pertussis. The fight to gain acceptance for vaccination against the illness was particularly difficult in the 1980s, when there were allegations, ultimately proven to be false, that the vaccine caused brain damage in some children.

Before a pertussis vaccine became widely available in the 1940s, the highly contagious infection sickened 200,000 children and caused 9,000 deaths each year in the United States. While the vaccine, a whole organism version known as DTP, significantly reduced the number of children hospitalized or killed by the disease, it did contain an endotoxin that caused side effects such as fever, pain and swelling at the injection site. When media reports based on faulty science linked the vaccine to infant encephalopathy in the 1980s, angry parents filed lawsuits and pharmaceutical companies began halting production of the vaccine. While he acknowledged the side effects of the vaccine’s endotoxin, Dr. Cherry strongly disputed claims that the vaccine caused brain damage. “It is time for the myth of pertussisvaccine encephalopathy to end,” he wrote in a Journal of the American Medical Association article and an editorial in The New York Times.

In response, anti-vaccination parent groups vilified him as a pawn of the pharmaceutical industry because he received grant money to study pertussis. “Someone wrote a book saying I was just about the worst person who ever lived,” Dr. Cherry recalls. “People testifying in lawsuits accused me of all kinds of things. I even received some calls and letters containing threats of harm.”

In 1991, an acellular version of the vaccine (DTaP), which contains only parts of the bacterium, replaced DTP. Dr. Cherry’s subsequent studies of DTaP showed the vaccine causes fewer side effects, but is less effective at producing immunity. Undeterred by a challenge, Dr. Cherry is now working on creating a new, genetically modified whole-organism version of the pertussis vaccine and has no qualms about stepping back into the fray. “There are always people who can make money out of criticizing vaccines, but I’m not worried about it,” Dr. Cherry says. “We think we know how to make a better vaccine.”