The number of whooping cough cases have more than quadrupled in the U.S. since last year, according to data reported by the Centers for Disease Control and Prevention on Friday.

Infectious diseases experts attribute the surge in cases of whooping cough — also known as pertussis — to a dip in vaccination rates that began during the pandemic.

“Children during COVID did not see their health care providers and they may have done some telemedicine, but we can’t vaccinate through the computer,” said Dr. William Schaffner, an infectious diseases specialist at the Vanderbilt University Medical Center. “And we haven’t gotten everyone caught up yet back to their routine vaccination levels.”

Whooping cough vaccines, called DTap and TDap and which also protect against diphtheria and tetanus, provide the most effective protection from the disease and its complications.

Previous research has fueled concerns about the short-lived effectiveness of whooping cough vaccines, with some experts voicing the need for new vaccines.

Reported cases of people with whooping cough are returning to pre-pandemic levels, when the U.S. typically saw more than 10,000 cases each year, the CDC said in July. The agency recorded 14,569 cases this year so far, an increase from the 3,475 total cases recorded last year.

Pennsylvania, New York and California lead all states in the number of cases, in that order. In Pennsylvania, 2,008 infections were recorded this year, almost double that of California.

Early symptoms of whooping cough can be mistaken for the common cold and other respiratory illnesses, which is why the disease often is not caught until it becomes severe.

That diagnostic challenge makes it easier to inadvertently spread, said Dawn Nolt, a professor of pediatric infectious diseases at Doernbecher Children’s Hospital in Portland, Ore.

“The first week or so of illness looks like any other respiratory disease,” she said, “when, in fact, it could be pertussis and you’re just infecting people around you.”

What sets whooping cough apart from other respiratory illness are the prolonged and fitful coughs, which last at least three weeks and can persist for many months, Nolt said. 

Irritated mucus membranes can cause often debilitating cough seizures, said Vanderbilt’s Schaffner.

“It’s not just one or two, it’s a whole series of coughs, so much so that you can’t breathe,” he said. “And when you finally, in a rather exhausted way, come to the end of your cough seizure, you inhale — that’s the ‘whoop.’ ”

Babies, however, may not cough as much but rather have difficulty breathing or intermittently stop breathing.

The CDC recommends the DTaP vaccine for babies and children under 7 years old. Older children and adults are advised to get the vaccine as well as a booster every 10 years.

The most severe cases are in infants, whose small airways can become more easily blocked, Schaffner said. Since babies can’t be vaccinated until they reach 2 months, the CDC recommends that pregnant people be vaccinated early in the last trimester of every pregnancy to protect newborns.