What to Know About Pertussis (Whooping Cough)

Pertussis, also called whooping cough or the 100-day cough, is a respiratory infection caused by Bordetella pertussis bacteria, which spreads through droplets when infected people cough and sneeze. The bacteria cause a person’s airways to swell and produce thick mucus, leading to severe, uncontrollable coughing fits, which end with a gasping “whoop” sound. 

“Pertussis is common, and highly contagious,” says Ruth Karron, MD, a professor in International Health. Approximately 90% of household contacts—family, roommates, and caregivers—who are exposed to someone with pertussis will become infected themselves. 

In the U.S., “we’re having a big resurgence of whooping cough right now,” Karron says. In 2025, there were nearly 28,000 pertussis cases, and about 36,000 cases in 2024—exceeding pre-pandemic averages. “Vaccination was always important, but it's even more important right now. It is the single most effective way of preventing pertussis in babies,” who account for 96% of whooping cough-related deaths.  

Because whooping cough often starts with cold-like symptoms, diagnosis can often be difficult or delayed until the infection progresses to more serious stages. Testing, especially after known exposure, is vital so that treatment can begin as early as possible. And since a person can be reinfected throughout their life, prevention is key.  

Who is most vulnerable to pertussis?

Infants under 6 months, especially newborns and babies younger than 3 months, are at the greatest risk of severe disease. Unlike slightly older children, when very young infants get pertussis, they may not have the characteristics ‘whoop’ after a prolonged bout of coughing. Instead, they may choke, gasp, or stop breathing altogether, which can cause them to turn blue. 

“Their brains can become deprived of oxygen, leading to seizures,” says Karron. Other complications include pneumonia, leukocytosis (elevated white blood cell count), pulmonary hypertension (high blood pressure in the lung arteries) and heart failure, hypoxemia (low blood oxygen), encephalitis (inflammation of the brain), and even death. 

Infants under 2 months of age diagnosed with pertussis should immediately be hospitalized, Karron says. “They need to be very closely observed and cared for with oxygen and antibiotics, because the risk of complications is so high.” 

What are the symptoms of pertussis?

It typically takes five to 10 days—though it can be as long as 21—after pertussis exposure for symptoms to appear. In the first one to two weeks, the symptoms are generally a runny nose, sneezing, mild fever, and a developing cough, or the infection could be asymptomatic, Karron says. “The characteristic symptom, the ‘whoop,’ doesn’t appear until the second stage, which can last from one to 10 weeks.” In the third phase, patients start to convalesce and recover, and the cough becomes less frequent and intense. Older children and adults may become asymptomatically infectious and transmit pertussis to others. 

How is pertussis diagnosed and treated?

Whooping cough is diagnosed primarily with a nasopharyngeal (nose and throat) swab tested by PCR to check for the presence of B. pertussis, as well as blood tests or a chest X-ray for complications like pneumonia. A lot of cases are missed, Karron says, because many people don’t seek clinical diagnosis. 

Treatment for pertussis focuses on early antibiotic therapy to reduce contagiousness and severity, along with rest, hydration, using a humidifier to help loosen thick mucus, and avoiding irritants like dust or smoke. Kids should not attend daycare or school, and adults should be home from work for five days after starting antibiotics. Severe cases require hospitalization for oxygen and IV fluids. Over-the-counter cough medicines are not effective at treating coughing associated with pertussis. 

How is whooping cough prevented?

Pertussis prevention primarily relies on two vaccines: DTaP for children under 7 years old, and Tdap for teens, adults, and pregnant people. Both vaccines also protect against diphtheria and tetanus. Very young children receive the shots in a series of doses. 

DTaP and Tdap are acellular vaccines, which use purified bacterial proteins to stimulate the body’s immune response. The downside is that “these vaccines provide very short-term immunity, and mostly against severe disease, not against infection,” Karron says. Nor do they prevent transmission from person to person: “Vaccination protects you against severe disease but doesn’t protect against infection,” she says. 

Whooping cough outbreaks tend to be cyclical, lasting from three to five years and driven primarily by the natural waning of immunity from both vaccines and prior infection. “You can get infected with pertussis multiple times in your life; neither vaccination nor actual infection protects you forever,” Karron says.  

Aside from vaccination, pertussis prevention relies on good hygiene like handwashing and covering coughs, masking, staying home while sick, and post-exposure antibiotics for close contacts, especially infants, to limit spread and protect vulnerable populations.  

Should I get vaccinated against pertussis while pregnant?

Pregnant people should get a booster during every pregnancy, “because we want that immunity to pass from mother to baby every time,” Karron says. “It is a critical part of prenatal care to get the Tdap vaccine.”  

While this won’t completely prevent infection in infants, it is highly effective against severe disease, hospitalization, and death in this age group. (In 2024, only about 60% of mothers in the U.S. got a Tdap vaccine during pregnancy.)  

Maternal vaccination for pertussis is highly safe and effective, with a decades-long record of no increased risk for adverse pregnancy or infant outcomes. For maximum protection, Tdap is recommended during the third trimester, which provides immediate immunity at birth and up to 2 months of age, when the newborn can be vaccinated with DTaP.  

Why is pertussis surging in the U.S.?

Like many respiratory diseases, whooping cough cases declined during the COVID-19 pandemic, likely due to safety measures such as masking and social distancing. Unable to jump from person to person, circulation of B. pertussis decreased, creating a population with lowered immunity to the disease. This, combined with disruptions in vaccination schedules and short-lived immunity from acellular vaccines, has allowed for larger, more widespread outbreaks as the pandemic waned.  

Vaccine hesitancy, which increased from 31% to 43% for maternal Tdap vaccines between 2019 and 2023, also plays a part. Contributing to this growing ethos of doubt is the persistent spread of misinformation about the safety of pertussis vaccines, as well as conflicting messaging from providers and health agencies. 

Before the 1940s, when the pertussis vaccine became widely used in the U.S., there were more than 200,000 cases a year. Since its implementation, numbers have decreased by more than 75%.  

“It’s a serious disease. It will roar back if we don’t immunize,” says Karron. “It's not like we've controlled it and it’s gone. We need to be vigilant; we need to continue to immunize our children, and we especially need to continue immunizing pregnant moms.”