Rates of whooping cough, like those of some other infectious diseases, declined soon after the start of the pandemic, as people wore masks and practiced social distancing, precautions that many have ceased, experts said. But during the early months of the pandemic, when people feared being exposed to the coronavirus in a doctor’s office, some children may have missed vaccination appointments, leaving them vulnerable to future infections.

Clusters of whooping cough cases have been reported in Kentucky, Oregon and western Pennsylvania, said C. Buddy Creech, director of the Vanderbilt Vaccine Research Program and a pediatric infectious-disease researcher for 20 years.

“This is still a terrible, terrible disease, one we’d do well to protect against,” Creech said.

Whooping cough, which draws its name from the sound the infected make when trying to breathe after coughing, begins much like an ordinary cold, causing sniffles and a cough. Patients can spread the disease through droplets before they are aware they have anything more serious than a cold.

The infection causes inflammation of the airways, and because those airways are much smaller in babies, their risk for severe illness is greater. As the disease progresses, the cough worsens, becoming spasmodic in serious cases. In China, the disease is sometimes known as the 100-day cough because it can persist for three months.

The illness, also known as pertussis, once killed about 9,000 Americans a year but tailed off substantially once vaccines became widely available in the 1940s. Today, up to 20 babies a year die from whooping cough, according to the Centers for Disease Control and Prevention.

The CDC said whooping cough cases declined over the past few years, during the covid-19 pandemic, but are starting to return to “pre-pandemic patterns,” which exceeded 10,000 cases a year.

Masking and remote learning during the pandemic probably lowered transmission of infectious diseases, such as pertussis, the agency said.

Rates of vaccination with the DTaP shot — which protects against diphtheria, tetanus and pertussis — declined substantially during the early wave of the pandemic, from March through September 2020. Vaccination rates otherwise have remained steady in recent years, according to the CDC.

From January 2023 through May 25, 2024, whooping cough caused 15 deaths in the United States, though the CDC declined to say how many of those deaths occurred this year citing “confidentiality reasons.”

England has also reported a substantial increase in whooping cough cases in the first three months of 2024, including the deaths of five infants.

Although the disease is best known for its toll on babies, the infection can cause serious illness in people older than 65, including rib fractures and significant pneumonia, Creech said.

In some cases, people who have not received a DTaP vaccine since childhood may contract whooping cough and experience moderate symptoms.

Jackie Marchbanks, 51, from central Oklahoma, started getting sick at the beginning of April with a sore throat, cough and a burning sensation in her eyes.

She said she “never dreamed it would have been whooping cough. I thought it was allergies.”

She tested multiple times for covid, but the tests came back negative. Weeks later, when she went to her primary care doctor, she was diagnosed with whooping cough.

Marchbanks, a nurse, said friends from other parts of the state have seen rising cases of adult whooping cough.

“That’s not a thing. That’s for kids. There are vaccines,” Marchbanks recalls thinking when she was diagnosed.

She was treated with steroids and antibiotics and said her symptoms began to subside after a few days.

The hardest-hit states this year include New York and Pennsylvania, both of which have reported about five times as many cases as they had at this point last year. Cases in North Carolina have risen sevenfold.

Increasing vaccinations during pregnancy is pivotal to slowing spread of the disease, experts said.

That’s because infants do not get vaccinated until two months of age; vaccination any sooner after birth is not effective. So protection in the first months of life comes from antibodies inherited in the womb. Vaccination between the 27th and 36th week of pregnancy provides strong protection from infection, said James Cherry, a distinguished professor of pediatrics at UCLA who has published studies of whooping cough. He said a separate whooping cough vaccination should be given during each pregnancy.

In one study of health-care workers at UCLA, Cherry and his colleagues found that about 6 percent were infected with pertussis a year. “Incredibly high, in fact so high, we had trouble believing it,” he said in a 2016 interview with the editor of the journal Open Forum Infectious Disease.

Despite the role vaccines play in slowing spread of infections and minimizing risk of severe disease, experts say skepticism and misinformation have contributed to a decline in immunization rates.

“We’ve seen decreasing vaccination rates, not just for covid, but across the board. Vaccines are our best way to prevent disease,” said Martha Buchanan, lead medical consultant and interim director for South Carolina’s Bureau of Communicable Disease Prevention and Control.

Nationally, 80 percent of children have received the DTaP shot. South Carolina has a vaccination rate of about 77 percent. The state has seen a modest rise in whooping cough cases, from 16 at this point in 2023 to 23 this year.

“Pertussis vaccine is a good vaccine, but if it’s not used, [disease] can spread like wildfire through a community,” said Robert W. Frenck Jr., an infectious-disease doctor at Cincinnati Children’s Hospital.

The pertussis vaccine, which is included in the DTaP shot, is highly effective at preventing whooping cough, which is caused by the bacterium Bordetella pertussis. The pertussis component of the vaccine is 98 percent protective within a year of children receiving the final dose, and 71 percent five years later, according to the CDC.

“If you look at the lives saved from vaccines and compare them to screenings for certain cancers, vaccines outpace all of them in terms of prevention of death,” said Frenck, who is also a member of the American Academy of Pediatrics committee on infectious diseases.

Vaccination during pregnancy has proven especially effective, Creech said, explaining, “Mom is actively pushing antibodies from her bloodstream into the baby.”

Infants are vaccinated at two months, four months and six months. Boosters are given at 15 to 18 months of age, then again right before entering kindergarten, and between the ages of 12 and 14.