Whooping Cough Resurgence: Why Pertussis Cases Are Rising Despite Vaccination

Why Is Whooping Cough Making a Comeback?

Pertussis, caused by the bacterium Bordetella pertussis, follows cyclical epidemic patterns with peaks every 3-5 years, but the 2024-2025 resurgence has been particularly notable. The CDC reported a significant increase in pertussis cases throughout 2024, with preliminary data indicating the highest annual case count since 2014, when approximately 32,971 cases were reported in the United States. Multiple countries, including the United Kingdom, Australia, and several European nations, have also reported substantial increases in pertussis activity.

The primary factor driving the resurgence is the waning immunity conferred by acellular pertussis vaccines. In the 1990s, the United States and most developed countries transitioned from whole-cell pertussis vaccines (wP) to acellular vaccines (aP) due to the higher rate of adverse reactions associated with whole-cell formulations, including fever, injection site reactions, and rare cases of encephalopathy. While acellular vaccines are significantly safer, studies have shown that their protection wanes more rapidly. A landmark 2012 study in the New England Journal of Medicine found that the odds of pertussis increased by approximately 42% for each year after the fifth DTaP dose, and that by 8-12 years after vaccination, protection was substantially diminished.

An additional contributing factor is that acellular vaccines, while preventing clinical disease, may be less effective at preventing colonization and transmission of B. pertussis. Research in baboon models published in PNAS demonstrated that acellular-vaccinated animals, when challenged with B. pertussis, did not develop disease but remained colonized and could transmit the bacterium to unvaccinated contacts. This suggests that vaccinated adolescents and adults may serve as asymptomatic or mildly symptomatic reservoirs, unknowingly transmitting pertussis to vulnerable infants who have not yet completed their primary vaccination series.

How Does Maternal Vaccination Protect Newborns from Pertussis?

Maternal Tdap vaccination is the cornerstone strategy for protecting newborns against pertussis, the age group at highest risk for severe disease, hospitalization, and death. The CDC, ACOG (American College of Obstetricians and Gynecologists), and WHO all recommend that pregnant individuals receive a dose of Tdap during each pregnancy, optimally between 27 and 36 weeks of gestation. This timing maximizes transplacental transfer of maternal anti-pertussis antibodies (particularly anti-pertussis toxin IgG) to the fetus, providing passive protection during the first 2-3 months of life.

The effectiveness of this strategy is well-documented. A 2017 study published in Clinical Infectious Diseases found that maternal Tdap vaccination was 91% effective at preventing pertussis in infants during the first two months of life and 69% effective through the first year. Data from the United Kingdom's maternal pertussis vaccination program, implemented in 2012 in response to a national outbreak, demonstrated vaccine effectiveness of approximately 90% against confirmed pertussis in infants under three months of age. Critically, maternal vaccination also reduced pertussis-related infant deaths by over 90%.

Despite strong evidence and recommendations, maternal Tdap vaccination coverage remains suboptimal. CDC data indicate that only approximately 55-60% of pregnant individuals in the United States received Tdap during pregnancy in recent years. Barriers include lack of provider recommendation, concerns about vaccine safety during pregnancy (which extensive safety data have not substantiated), and missed opportunities during prenatal care visits. Increasing maternal vaccination rates is considered the single most impactful intervention for reducing infant pertussis morbidity and mortality.

What Are the Symptoms of Pertussis and When Should You Seek Medical Care?

Pertussis has an incubation period of 5-21 days (typically 7-10 days) and progresses through three distinct clinical stages. The catarrhal stage lasts 1-2 weeks and is characterized by mild cold-like symptoms including rhinorrhea, mild cough, low-grade fever, and sneezing. This stage is when the disease is most contagious but least recognized, as symptoms are indistinguishable from a common upper respiratory infection. During this window, B. pertussis is most readily transmitted through respiratory droplets.

The paroxysmal stage, lasting 2-8 weeks or longer, is the hallmark of the disease. It is characterized by episodes of rapid, violent coughing fits (paroxysms) that can last for several minutes and may be followed by a high-pitched inspiratory whoop, post-tussive vomiting, or exhaustion. In infants, the whoop may be absent, and apnea (cessation of breathing) may be the primary manifestation, making the disease particularly dangerous in this age group. Adults and vaccinated individuals often present with a prolonged cough lasting more than two weeks without the classic whoop, making diagnosis challenging.

Medical care should be sought if someone experiences a cough lasting more than two weeks, coughing fits followed by vomiting, difficulty breathing or apnea (especially in infants), or a whooping sound during inhalation. Pertussis is treated with macrolide antibiotics (azithromycin, clarithromycin, or erythromycin), which are most effective when started during the catarrhal stage but are still recommended during the paroxysmal stage to reduce transmission. Close contacts should receive prophylactic antibiotics regardless of vaccination status. Infants under one year of age and particularly those under four months are at the highest risk for complications including pneumonia, seizures, encephalopathy, and death, and should be monitored closely in a hospital setting.

What Booster Vaccines Are Available and Who Should Get Them?

The Advisory Committee on Immunization Practices (ACIP) recommends a comprehensive pertussis vaccination schedule to maintain population immunity. Children receive a five-dose DTaP series at ages 2 months, 4 months, 6 months, 15-18 months, and 4-6 years. Adolescents should receive a single dose of Tdap at age 11-12 years, which serves as their first adult booster. Adults aged 19 and older who have never received Tdap should receive a single dose, regardless of when they last received a Td (tetanus-diphtheria) vaccine.

Of particular importance is the recommendation for Tdap during each pregnancy, ideally administered between 27 and 36 weeks of gestation. Healthcare workers, childcare providers, and anyone who will have close contact with infants under 12 months of age should also ensure they are up to date on their Tdap vaccination. This cocooning strategy aims to reduce the risk of transmission to vulnerable newborns by vaccinating those in their immediate environment.

Research into next-generation pertussis vaccines is ongoing. Several groups are developing improved acellular vaccines with novel adjuvants that may induce longer-lasting immunity and better mucosal protection. Live attenuated nasal pertussis vaccines, such as BPZE1 developed by ILiAD Biotechnologies, aim to mimic natural infection to generate more robust and durable immune responses, including mucosal immunity that could prevent colonization and transmission. Additionally, whole-cell pertussis vaccines with improved safety profiles are being reconsidered for use in some settings, as countries that continued using whole-cell vaccines (such as Japan, which switched back to wP for the first dose) have generally experienced fewer pertussis resurgences.