After a long day in the laboratory in 1932, Pearl Kendrick and Grace Eldering walked out into the chilly Michigan evening with specially prepared petri dishes, called cough plates, in tow. The two scientists were on a mission to collect bacteria in the wild: one by one, they visited families ravaged by whooping cough, the deadliest childhood disease of their time. By the dim light of kerosene lamps they asked sick children to cough onto each plate, dimpling the agar gel with tiny specks of the bacteria Bordetella pertussis.

As they collected their research samples from “whooping, vomiting, strangling children,” Kendrick and Eldering, both former school teachers who lived together in Grand Rapids, “listened to sad stories told by desperate fathers who could find no work,” Eldering later recalled. “We learned about the disease and the Depression at the same time.”

Using cultures from the suffering children that they “saved and studied in every possible way,” the pair created the first effective vaccine for whooping cough after years of toiling in their lab, growing and identifying pertussis strains from cough plates. Developed at a time when scientific funding was so scarce that lab mice were considered a luxury, the vaccine would go on to prevent thousands of children each year from succumbing to the disease.

In the 1940s, Kendrick and Eldering's lab also developed the vaccine that most people receive today, called DTP, that protects against diphtheria and tetanus as well as whooping cough, alongside an African-American female chemist named Loney Gordon. This became a staple early-life vaccine, multiplying the survival rate of children in the United States as it spread across the country.

Back when Eldering and Kendrick began working on their vaccine in the 1930s, an estimated 6,000 kids in the United States were dying from whooping cough, or pertussis, each year—more than from diphtheria, scarlet fever, tuberculosis or polio. Once infected, victims make a characteristic “whoop” coughing sound as their bodies fight the bacteria. In a vicious cycle, the cough spreads the contagion to others, and is so powerful that it can induce shaken baby syndrome. Babies who get it have a high chance of dying.

“It’s difficult to explain just how desperate people were for a [whooping cough] vaccine at this time,” says historian Carolyn Shapiro-Shapin, who has extensively researched Kendrick and Eldering.

As whooping cough ravaged the Grand Rapids area, Kendrick and Eldering worked around the clock to battle the highly contagious disease. They knocked on doors, analyzed samples, and later recruited locals for field trials of the vaccine. Incredibly, the original 1930s vaccine work began as a side project for Kendrick and Eldering, who both worked in a laboratory at the Michigan Department of Health.

“It was done on top of everything else. When the work day was over, we started on the research,” Elderick told the Grand Rapids Press in 1984. We’d come home, feed the dogs, get some dinner, and get back to what was interesting.”

The scientists were motivated by personal experience. Both women had survived whooping cough as children (Kendrick in New York, Eldering in Montana) and knew firsthand how painful the disease was. “I think anyone who ever had whooping cough or had seen it feared it,” Eldering said in the Grand Rapids Press. “I still remember the terrible spells of coughing that came on. I coughed until I thought it would be the end.”

While scientists had tried to make whooping cough vaccines since 1914, the vaccines available were not very effective; no one was sure how much or which strain of the bacteria was best to use, and it was difficult to grow in the lab. By 1931 the American Medical Association Council on Pharmacy and Chemistry believed “the pertussis vaccines seem to have absolutely no influence.”

It would take two former school teachers, well versed in dealing with terrified children and making budgets stretch, to take the first consequential steps toward defeating the disease. Scientific funding was rarely given before World War II, but when the pair discovered that First Lady Eleanor Roosevelt was visiting Grand Rapids, they invited her on a laboratory tour. Roosevelt not only accepted, but actively learned about their work for hours; afterward she helped the scientists secure rare federal funding.

READ MORE: How the Great Depression Affected Working Women

“Kendrick and Eldering were very good at working on shoestring budgets. The fact that they had mice to use for their research at all tells you how important it is, because most of the mice available had been pulled for penicillin research,” says Shapiro-Shapin.

Kendrick and Eldering’s friendship likely got them through many long, tiring nights in the lab stirring vats of raw materials. In the 1930s, science research was, to put it mildly, low tech compared with today. Now, if scientists need to grow a microbe, they can buy an instant powder made of potato starch or agar to use as a medium. In Kendrick and Eldering’s day, mediums were made from scratch by boiling "the potatoes and seaweed yourself,” says Shapiro-Shapin.

The repetitive nature and low pay of biological research is likely why public health-related sciences were often associated with “so-called women’s work” in the 1930s, says Shapiro-Shapin. Many male scientists focused on other areas, which inadvertently opened the door for dedicated women in the field.

“It’s a field which seemed particularly to appeal to women, and in which women excelled,” Kendrick told the Grand Rapids Press in 1975.

Kendrick and Eldering were not typical research biologists, however; they were extremely adept public organizers. They persuaded nurses and doctors to volunteer as lab workers, and persuaded residents to participate in a large-scale trial. Through the Department of Health, the two scientists coordinated with women’s groups, parent-teacher associations and health clinics.

By the time Kendrick and Eldering were ready to begin the full field trial of their vaccine in 1934, parents had already volunteered their children in droves. The results were impressive; in the first run of the Grand Rapids trials, only three vaccinated children out of 1,592 in the study developed whooping cough, versus 63 non-vaccinated children. During the trial’s three-year run, 5,815 children were given the vaccine against a control group of randomly selected unvaccinated children, and roughly 90 percent of the vaccinated children in the program avoided contracting the disease. Local doctors, schools and health departments began using the whooping cough vaccine, which was distributed and used across Michigan and by the American Academy of Pediatrics.

READ MORE: Why It Took So Long to Eliminate Measles

Kendrick and Eldering continued working with the Grand Rapids community through the 1940s, hiring and working alongside more brilliant woman scientists in the increasingly female public health field. After World War II, Kendrick and Eldering recruited chemist Loney Clinton Gordon. Gordon improved on Kendrick and Eldering’s work by testing thousands of pertussis cultures for the optimal strain for the final iteration of their vaccine; in a 1999 interview, Gordon said, ”when I found out that was the organism I was just ecstatic. I was crazy with joy and happiness.”

With Gordon’s contributions, Kendrick and Eldering’s laboratory created an updated, combined vaccine DTP for diphtheria, tetanus and pertussis (now DTaP), allowing parents to safely vaccinate their children against multiple diseases at once. Kendrick later became a major voice in public health worldwide, setting up vaccine initiatives with OSHA and the World Health Organization. Their work also sparked a lifelong friendship; Kendrick and Eldering lived together until Kendrick's death in 1980.

Despite the success of the first effective whooping cough vaccine, its creators' renown may have been eclipsed by the fact that it was released during the Great Depression and then updated during World War II. Later in her life, Eldering reflected to the Grand Rapids Press that there would have “been an explosion” of press had the vaccine been developed at another moment.

A recent rise in families who choose not to vaccinate has led to some whooping cough outbreaks, but, overall, the vaccines developed by Kendrick, Eldering and Gordon have vastly increased the U.S. life expectancy for children. Their determination to help suffering kids at the peak of the Depression changed the United States so drastically that most living today will never know the horrors of the “100 day cough.”