Pertussis, commonly known as whooping cough, is far more common than most people realize. The CDC reported 7,063 cases in the United States in 2023, but that number likely represents only a fraction of actual infections. Research estimating true incidence suggests the real number of cases could be 58 to 93 times higher than what gets formally diagnosed, putting the actual burden in the hundreds of thousands annually in the U.S. alone.
Reported Cases in the United States
Official case counts have fluctuated dramatically over the past several years. In 2019, before the pandemic, the U.S. recorded 18,617 cases. That number dropped sharply during the COVID-19 era, likely due to masking, social distancing, and reduced testing. Cases hit a low of 2,116 in 2021, then began climbing: 3,044 in 2022 and 7,063 in 2023.
Then 2024 saw a major surge. Preliminary CDC data show more than six times as many cases were reported in 2024 compared to 2023, exceeding even pre-pandemic levels. Cases peaked around November 2024 and have been trending down since, but numbers remain elevated compared to the years immediately before the pandemic. This kind of rebound was expected by public health officials, since routine childhood vaccinations were disrupted during COVID and pertussis tends to build up in cycles.
The Global Picture
Worldwide, the WHO reported 941,565 pertussis cases in 2024. But official tallies drastically undercount the real burden, especially in countries with limited surveillance. A widely cited 2014 estimate put the true global figure at roughly 24.1 million cases per year, with about 160,700 deaths in children under 5. Most of those deaths occur in low-income countries where vaccination coverage is inconsistent.
Why Cases Come in Waves
Pertussis doesn’t maintain a steady level. It surges in epidemic cycles every 3 to 5 years, and this pattern existed before vaccines and has persisted ever since. The cycles happen because immunity, whether from vaccination or a previous infection, fades over time. As the number of susceptible people in a population gradually increases, conditions ripen for an outbreak. Once enough people get infected, the cycle resets.
Vaccination didn’t eliminate this cyclical pattern, but it did dramatically reduce the baseline. Since widespread vaccine use began, pertussis incidence has dropped more than 75% compared to the pre-vaccine era, when the U.S. saw over 100,000 reported cases per year. Maintaining herd immunity against pertussis requires very high vaccination coverage, estimated at 92% to 94%, which is a difficult threshold to sustain given that vaccine protection wanes within several years of each dose.
Most Cases Go Undiagnosed
The gap between reported pertussis and actual pertussis is enormous. A study estimating true incidence among Americans under 50 found an overall rate of about 649 infections per 100,000 people per year. That’s roughly 72 times higher than the rate based on formally diagnosed cases. The ratio varied between 58 and 93 times higher depending on the year.
This massive undercount happens for several reasons. In older children, teens, and adults, pertussis often doesn’t look like the classic “whooping cough” seen in infants. It can present as a persistent cough lasting weeks, sometimes without the telltale whooping sound. Many people never see a doctor for it, and even those who do are frequently diagnosed with bronchitis or a generic upper respiratory infection. Without a specific lab test, pertussis in adults easily flies under the radar.
Who Gets Hit Hardest
Infants under 1 year old bear the highest reported rate of pertussis by a wide margin. In 2023, the incidence rate for babies under 1 was 23.16 per 100,000, compared to just 0.76 per 100,000 for adults over 20. That 30-fold difference reflects both genuine vulnerability and the fact that infant cases are more likely to be recognized and reported because they’re more severe.
About 27% of pertussis patients under age 1 end up hospitalized. The youngest infants face the greatest danger: babies under 2 months old accounted for just 1.6% of all reported cases in one large CDC analysis, but nearly 30% of all hospitalizations. These newborns haven’t yet received their first vaccine dose and rely entirely on antibodies passed from their mother during pregnancy. Adults over 65 also face elevated risk, with about 12% requiring hospitalization.
For older children and healthy adults, pertussis is rarely dangerous but can be miserable. The cough often lasts 6 to 10 weeks, sometimes longer, earning it the nickname “the 100-day cough.” Coughing fits can be severe enough to cause vomiting, rib fractures, or fainting. Deaths are rare outside of very young infants and elderly adults, but the sheer duration of illness makes it one of the more disruptive common infections.
Why Pertussis Persists Despite Vaccination
Pertussis is unusually difficult to control compared to other vaccine-preventable diseases. The current vaccines used in the U.S. and most high-income countries provide strong initial protection, but that protection fades faster than it does for diseases like measles or polio. By 5 to 10 years after the last booster, protection has dropped significantly. This means that teenagers and adults, even those who were fully vaccinated as children, can become susceptible again and serve as a reservoir that spreads the bacterium to vulnerable infants.
The herd immunity threshold for pertussis sits at 92% to 94%, which is among the highest of any infectious disease. Current vaccines, while effective at preventing severe illness, fall just short of reliably reaching that threshold at a population level. Combined with waning immunity and cyclical dynamics, this explains why pertussis continues to circulate even in countries with strong vaccination programs. It’s not a failure of vaccination so much as a reflection of how challenging this particular bacterium is to eliminate.