NEW YORK — In the first study of its kind, researchers Monday confirmed that a mother’s beneficial microbes can be transferred, at least partly, from her vagina to her baby after a caesarean section.

The first microbes to colonize a newborn delivered vaginally come almost exclusively from its mother. But the first to reach an infant born by caesarean section come mostly from the environment, including hard-to-clean areas such as lamps and walls, and skin cells from others in the delivery room.

That difference, some experts believe, could influence a child’s lifelong health.

The new study suggests a new way to inoculate babies, said Dr. Maria Gloria Dominguez-Bello, an associate professor of medicine at New York University and lead author of the report, published Monday in Nature Medicine.

“The study is extremely important,’’ said Dr. Jack Gilbert, a microbial ecologist at Argonne National Laboratory who did not take part in the work. “Just understanding that it’s possible is exciting.’’

But it will take further studies following C-section babies for many years to know to what degree, if any, the method protects them from immune and metabolic problems, he said.

Some epidemiological studies have suggested that C-section babies may have an elevated risk for developing immune and metabolic disorders, including Type 1 diabetes, allergies, asthma, and obesity.

Scientists have theorized that these children may be missing key bacteria known to play a large role in shaping the immune system from the moment of birth onward. To replace these microbes, some parents have turned to a novel procedure called vaginal microbial transfer.

A mother’s vaginal fluids — loaded with one such essential bacterial strain, lactobacillus, that helps digest human milk — are collected before surgery and swabbed all over the infant a minute or two after birth.

An infant’s first exposure to microbes may educate the early immune system to recognize friend from foe, Dominguez-Bello said.

Friendly bacteria, like lactobacilli, are tolerated as being like oneself. Those from hospital ventilation vents or the like may be perceived as enemies and be attacked.

These early microbial interactions may help set up an immune system that recognizes “self’’ from “non-self’’ for the rest of a person’s life, Dominguez-Bello said.

In the United States, about 1 in 3 babies are delivered by C-section, a rate that has risen dramatically in recent decades. Some hospitals perform the surgery on nearly 7 in 10 women delivering babies.

An ideal C-section rate for low-risk births should be no more than 15 percent, according to the World Health Organization.

New York Times