Colorado sees increase in whooping cough cases after dropping to pandemic-era lows

DENVER — Whooping cough, also known as pertussis, is making a comeback in Colorado after dropping to pandemic-era lows.

State health officials said more than 930 cases were reported each year in 2024 and 2025.

Colorado Department of Public Health & Environment Whooping cough cases in Colorado by year

“The 2025 data is preliminary, so final 2025 case counts may change,” a spokesperson for the Colorado Department of Public Health and Environment said.

CDPHE said about two-thirds of the state's whooping cough cases involve people under 18.

“We’ve seen quite a rise in pertussis cases in our community,” Dr. Stephanie Harris, Kids First Pediatrics, said.

Dr. Harris has been a pediatrician in Lakewood for nearly three decades. She said local cases have increased by more than 600% since 2006.

“In most of these outbreaks that we have seen lately, the majority of the children have been unvaccinated,” Dr. Harris said.

► Watch Sophia Villalba's report in the player below:

Colorado sees increase in whooping cough cases after dropping to pandemic-era lows

State health officials said school vaccination rates have declined since the pandemic.

“Based on school and childcare data for 2024-2025, vaccination rates for DTaP and Tdap have decreased by 2.9% and 3.3%, respectively, since the 2019-2020 school year,” CDPHE said.

Centers for Disease Control and Prevention Bordetella pertussis

But officials said another factor is waning immunity. 73% of the reported cases in 2025 were vaccinated people.

"Breakthrough cases can occur in fully vaccinated individuals because immunity from both childhood vaccines (DTaP vaccine series) and adolescent/adult boosters (Tdap) naturally wanes over time," CDPHE told Denver7.

“If kids don’t get their booster doses. " It can put them at higher risk of contracting the disease,” Dr. Harris said.

Some parents said the trend is especially concerning for their own kids.

“I have two young school-age kids. Obviously, this is something to be concerned about, especially because that's something that affects primarily young children,” Derick Vranizan, a parent in Denver, said.

“Being in close contact in a schoolroom setting or a workplace setting could definitely spread the disease among multiple people,” Dr. Harris added.

For Derick Vranizan, being well-informed is key.

“My wife and I rely heavily on our pediatrician to advise us, and we've taken that course with both kids,” Vranizan said.

Doctors said that while vaccinated children can still get sick, their cases are often less severe.

“Vaccination really is the best prevention,” Dr. Harris told Denver7.

Centers for Disease Control and Prevention Whooping Cough vaccines

Dr. Harris added that anyone who has not received the whooping cough vaccine within the last 10 years is at a higher risk of catching the disease.