Can You Get Pertussis After the Vaccine?

Pertussis vaccination substantially lowers your risk of whooping cough, but it does not eliminate it. Protection fades over time, and breakthrough infections in vaccinated people are well documented. One large review found that the acellular pertussis vaccine starts at roughly 80% effectiveness in the first year but drops to about 41% after eight or more years.¹ The reasons behind this go beyond simple “wearing off” and involve some genuinely surprising biology worth understanding.

How Quickly Protection Fades

The pertussis vaccines used in the United States, Canada, Australia, and most of Europe since the 1990s are acellular formulations, meaning they contain a handful of purified proteins from the bacterium rather than the whole killed organism. These replaced the older whole-cell vaccines primarily because the whole-cell versions caused more side effects like fever and injection-site swelling.² The tradeoff, which took years to become clear, was durability.

A study tracking children after their fifth dose of acellular pertussis vaccine (the one typically given before starting school) found the odds of getting pertussis rose by about 42% with each passing year.³ That means a 12- or 13-year-old who last received a pertussis shot at age five has dramatically less protection than a six-year-old who just got theirs. This timeline helps explain the characteristic surge in pertussis cases among preteens and teenagers.

For adults, the picture is similar. A single Tdap booster raises antibody levels effectively, and one dose appears sufficient to restore protection in the short term.⁴ But without periodic re-boosting, those antibodies decline along the same trajectory seen in children, leaving adults vulnerable again within several years.

The Whole-Cell Versus Acellular Gap

One of the more striking findings in pertussis research is just how differently the two vaccine types perform over the long run. A large U.S. cohort study found that children who received only acellular pertussis vaccines had roughly 8.5 times the risk of pertussis compared with children who had received at least one dose of the older whole-cell vaccine.⁵ Even a single whole-cell dose early in the series appeared to extend the protection provided by later acellular boosters.

Population-level data bear this out. After the U.S. completed its switch from whole-cell to acellular vaccines, pertussis case counts rose significantly. An analysis adjusting for vaccination coverage estimated that, on average, over 16,000 more pertussis cases per year were seen after the full transition compared to the whole-cell era.⁶ Many countries that still use whole-cell vaccines in their primary infant series have not experienced the same degree of resurgence, though direct comparisons are complicated by differences in surveillance and reporting.

A Swedish study of long-term follow-up found both vaccine types holding up well over six years, with about 89% efficacy for the acellular and 92% for the whole-cell formulation.⁷ The real divergence tends to show up beyond that window, which is why waning became apparent only after entire birth cohorts grew up on acellular-only schedules.

Why Acellular Vaccines Let the Bacteria Through

The mechanism behind this gap goes deeper than antibody levels. Acellular pertussis vaccines train your immune system to recognize a few specific proteins, and they do a good job stimulating blood-borne antibodies. What they do poorly, compared to whole-cell vaccines, is trigger the mucosal immune defenses in the nose and throat where the pertussis bacterium actually sets up shop.

Research in animal models has shown that acellular vaccines protect against symptoms but fail to prevent the bacteria from colonizing the airways. In a primate study, baboons vaccinated with the acellular vaccine were shielded from severe whooping cough but still carried the bacteria just as long as unvaccinated animals and readily spread the infection to others.⁸ The whole-cell vaccine, by contrast, generated mucosal immune responses that helped clear the bacteria from the nose and throat more effectively.

Mouse studies have pointed to a specific gap: acellular vaccines produce weak mucosal memory cells in the airways. Tissue-resident memory cells from acellular-vaccinated animals were poorly activated when exposed to pertussis, while those from whole-cell-vaccinated animals mounted a strong response.⁹ A synthesis of this research argues that the ability to induce mucosal immunity that blocks or shortens airway carriage is fundamentally what distinguishes the two vaccine types and may explain much of the pertussis resurgence in countries that adopted acellular formulations.¹⁰

The practical takeaway is uncomfortable: a vaccinated person can become silently infected, carry the bacteria in their airways, and pass it to a vulnerable infant or unvaccinated contact without ever realizing they are sick. This is not a failure of vaccination so much as a limitation of the current vaccine design.

The Bacterium Is Adapting, Too

Beyond waning immunity and limited mucosal protection, the pertussis bacterium itself is changing in ways that blunt vaccine effectiveness. Acellular vaccines target a small set of bacterial surface proteins, and one of the most important is called pertactin. In the United States, the vast majority of circulating pertussis strains have now acquired mutations that disable pertactin production. These mutations arose independently in different lineages, which is strong evidence that vaccine-induced immune pressure is driving the change.¹¹

Globally, countries that switched to acellular vaccines have seen pertactin-negative strains exceed 85% of clinical isolates in some cases.¹² This does not mean the vaccines are useless against these strains. The vaccines contain other antigens that still trigger protective responses. But losing a major target does chip away at overall effectiveness, and it raises a legitimate question about how much further the bacterium can evolve under current vaccine pressure.

What Breakthrough Pertussis Actually Looks Like

If you do get pertussis after being vaccinated, the illness is typically shorter and less severe than what an unvaccinated person experiences. A study in Oregon during a pertussis outbreak found that vaccinated patients were about 80% less likely to be hospitalized and roughly 60% less likely to develop severe illness compared to unvaccinated patients. They also stopped coughing significantly sooner.¹³

That milder presentation is both good news and a diagnostic problem. In adults especially, breakthrough pertussis often looks like a stubborn cough that lingers for weeks without the dramatic “whoop” that gives the disease its name. One study of adults with prolonged coughs found that about one in five had laboratory evidence of pertussis infection, yet fewer than 1% had positive culture or PCR results, meaning most cases were picked up only through antibody testing.¹⁴ A substantial proportion of hospitalized adults with a cough lasting two or more weeks show serological signs of pertussis that often get misdiagnosed as pneumonia or chronic obstructive lung disease.¹⁵

Diagnostic testing itself is complicated by vaccination history. Culture and PCR work best in the first couple of weeks, before antibiotics and the immune response have suppressed bacterial numbers. By the time most adults seek care for a persistent cough, the window for those tests has often closed. Serology can catch later cases but cannot reliably distinguish between a recent infection and a recent vaccination.¹⁶ Health professionals are encouraged to maintain a high index of suspicion for pertussis in anyone with a cough lasting more than two weeks, even between outbreaks.¹⁷

Can Pertussis Be Eradicated With Current Vaccines?

Almost certainly not. A modeling study using Swedish data estimated that, even before immunity wanes, the acellular vaccine gives a vaccinated person only about a 58–63% chance of resisting infection when exposed. Combined with the bacterium’s relatively low transmissibility threshold, that level of individual protection is not enough for mass vaccination to push the disease to extinction.¹⁸ For comparison, measles vaccines confer over 95% protection against infection, which is why measles eradication is at least theoretically possible. Pertussis, with the tools currently available, is not.

This does not mean vaccination is pointless. Widespread pertussis vaccination dramatically reduces severe illness, hospitalization, and death, especially in young infants. But expecting it to stamp out the disease entirely sets up an unrealistic benchmark against which any outbreak looks like a vaccine failure.

Protecting Newborns Before Their Own Shots Kick In

The most dangerous period for pertussis is the first few months of life, before an infant has received enough vaccine doses to build protection. Vaccinating pregnant women with Tdap during the third trimester helps bridge this gap. The mother produces antibodies that cross the placenta, giving the newborn a temporary buffer. Infants born to vaccinated mothers have significantly higher antibody levels at birth and at two months compared to those born to unvaccinated mothers.¹⁹ A randomized trial confirmed that third-trimester immunization results in cord blood antibody concentrations that may cover the period of highest risk.²⁰

There is an interesting wrinkle, though. The antibodies a mother transfers depend partly on what kind of pertussis vaccine she received as a child. Women who were themselves primed with whole-cell vaccine as infants pass along higher levels of the antibody considered most protective against severe infant disease than women who received only acellular vaccine growing up.²¹ As the generation of women who received whole-cell vaccines ages out of childbearing years, the passive protection afforded to newborns through maternal vaccination could diminish. This is a population-level concern that health authorities are watching closely.

An alternative strategy, sometimes called cocooning, involves vaccinating everyone in close contact with a newborn. Cost-effectiveness analyses suggest that vaccinating the mother during pregnancy protects infants more efficiently than the cocoon approach. One Spanish analysis estimated that about 1,330 pregnant women would need to be vaccinated to prevent one infant hospitalization, compared to nearly 4,750 parents in a cocooning strategy.²²

What to Do If You Have Been Exposed

If you find out you have been in close contact with someone who has pertussis, antibiotics given soon after exposure can reduce your chance of developing the disease, even if you are fully vaccinated. This post-exposure prophylaxis, usually a short course of azithromycin, is particularly recommended for household contacts of a confirmed case. In a U.S. evaluation, uptake of prophylaxis among household contacts was high, and none of the contacts who completed the course developed symptomatic pertussis during follow-up.²³ The same study found that modest delays in starting antibiotics did not appear to increase transmission within households, though getting started early is still the general recommendation.

A Related Bacterium the Vaccine Doesn’t Cover

There is a cousin of the pertussis bacterium called Bordetella parapertussis that causes a clinically similar cough illness, sometimes indistinguishable from true whooping cough. Current pertussis vaccines provide no meaningful protection against it. A meta-analysis of over 46,000 participants found no significant protective effect of pertussis vaccination against B. parapertussis infection.²⁴

The reason is biological, not an oversight. B. parapertussis carries a surface structure called an O antigen that shields it from antibodies generated against B. pertussis. Even natural infection with pertussis does not cross-protect against its cousin.²⁵ A rodent study went further, finding that acellular vaccination actually increased B. parapertussis bacterial counts in the lungs by roughly 40-fold compared to unvaccinated animals, possibly because vaccine-induced immune responses disrupted the natural competition between the two species.²⁶ Whether this translates to the same effect in humans is not established, but it is a reminder that whooping-cough-like symptoms after vaccination may sometimes be caused by an entirely different organism that no current vaccine addresses.

Next-Generation Vaccines on the Horizon

Researchers are working on pertussis vaccines designed to overcome the limitations of current acellular formulations. The most prominent approach is a live attenuated nasal vaccine called BPZE1, which is a weakened form of the actual bacterium delivered as a nasal spray. The idea is to mimic natural infection closely enough to trigger the mucosal immune response that acellular injections miss. In an early clinical trial, about 81% of vaccinated participants showed nasal colonization by the weakened strain, and the vaccine produced increases in both blood-borne and mucosal antibodies that persisted out to 12 months.²⁷ Later-stage trials are still needed, but the early results suggest this approach could address the colonization-and-transmission blind spot that current vaccines leave open.

Other strategies under investigation include reformulated acellular vaccines with broader antigen coverage, adjuvants designed to steer the immune response toward mucosal protection, and outer-membrane vesicle vaccines that present a wider array of bacterial surface features. None of these is close to replacing the current vaccines on the immunization schedule, but the recognition that acellular pertussis vaccines have a fundamental design limitation has motivated a level of research activity that was not present a decade ago.