Whooping cough cases are rising, and doctors are bracing for yet another tough year.

There have been 8,485 cases reported in 2025, according to preliminary data from the U.S. Centers for Disease Control and Prevention. That’s twice as many cases as this time last year, based on the CDC’s final tally.

Rates of whooping cough, or pertussis, soared last year, which experts said wasn’t unexpected. The number of cases fell during COVID-19 because of masking and social distancing.

But experts say the outbreaks of vaccine-preventable illnesses, like measles and whooping cough, could be indicative of changing attitudes toward vaccines. U.S. kindergarten vaccination rates fell last year, and the number of children with vaccine exemptions hit an all-time high.

Whooping cough tends to peak around this time of year and in the fall. It’s usually spread through respiratory droplets in the air, when people with pertussis cough, sneeze or breathe close to others. The symptoms are similar to a cold but the cough becomes increasingly severe with a distinctive sound — a “whoop” as the person tries to take in air. It is treated with antibiotics.

The pertussis vaccine, which also protects against diphtheria and tetanus, is given at two months, four months and six months. The CDC recommends adults get follow-up doses every 10 years.

The illness is most dangerous for infants, especially before they receive their first round of vaccinations. That’s why the vaccine is also recommended for expecting mothers to protect newborns.

Pennsylvania, one of the states hit hardest by the illness last year, has recorded 207 whooping cough cases in 2025.

Neil Ruhland, a state health department spokesman, said the biggest increases are in populated areas like Philadelphia and Pittsburgh and in middle and high schools and colleges. He said 94.6% of the state’s kindergarten students are vaccinated.