Can Vaccinated Individuals Be Silent Carriers of Pertussis? What Every Expecting Family Should Know

For years, pertussis (whooping cough) has been a major concern for expecting parents, providers, and newborn care teams. While vaccination remains a standard recommendation, emerging immunology research has revealed an important nuance about how pertussis vaccines work; especially the modern acellular pertussis vaccines (aP) used in Tdap and DTaP.

Understanding this science empowers families to make informed decisions and invites a deeper question:

If a vaccine prevents symptoms but not infection or transmission, are we fully addressing the problem or simply masking it?

Acellular Pertussis Vaccines: What They Do and What They Don’t Do

Modern pertussis vaccines, including Tdap, are claimed to provide strong systemic immunity that protects individuals from severe illness. Even highly recommended for pregnant mothers to pass supposed immunity to their baby.

But the scientific literature is consistent on one point: aP vaccines do not reliably prevent colonization or asymptomatic infection.

This raises a logical contradiction worth acknowledging:

• If a person can still carry and spread pertussis after vaccination, is vaccination the key to protect newborns?

• Or are we unintentionally creating a population that can spread pertussis silently?

Silent Carriage: The Scientific Reality

Mechanistic studies from PNAS, Nature Immunology, Vaccine, Pediatrics, and Journal of Infectious Diseases reveal that:

aP vaccines generate excellent systemic IgG antibodies, but weak mucosal IgA and Th17 immunity, leaving the nose and throat open to temporary colonization.

This is why vaccinated individuals may feel perfectly well while carrying pertussis.

And this brings up another uncomfortable question:

If the vaccinated can spread pertussis without symptoms, why is the unvaccinated population often framed as the primary threat?

Where Tdap Fits In And What Often Goes Unsaid

Pregnant people are strongly encouraged to receive Tdap in the third trimester. Said to protect babies through passive antibodies..

Tdap creates silent carriers.

Tdap does not reliably block nasopharyngeal colonization; this can allow asymptomatic carriage and potentially transmission, which is the scientific basis for calling such individuals “silent carriers.”

That conclusion is supported by high-quality experimental evidence and multiple reviews, though population-level human carriage prevalence estimates vary by study.

Mechanistic and epidemiological evidence shows that the aP vaccine platform does not reliably create strong mucosal immunity (local IgA and Th17 responses in the upper airway).

Because mucosal immunity is what prevents colonization, this creates a physiologic gap:

Even when protected from symptoms, a person vaccinated with Tdap/DTaP may still carry Bordetella pertussis in the nasopharynx.

This is known as colonization without disease or asymptomatic carriage/silent carriage.

Why this matters in pregnancy and early newborn life:

• Pregnant people often receive Tdap in the third trimester (as recommended) to protect the baby through passive antibodies.

• Those antibodies are supposed to protect the newborn from severe disease, but they do not prevent exposure if someone around the infant is carrying pertussis asymptomatically.

• Since aP vaccines (including Tdap) can prevent symptoms without fully preventing nasal colonization, family members, siblings, or caregivers can appear completely healthy yet still carry and shed the bacteria.

• Newborns have immature immune systems and are at highest risk for complications like apnea, pneumonia, ICU admission, or death even after mild exposure from an adult who shows no symptoms.

• The overseeing organizations are aware of these contradictions. Yet Tdap is still strongly recommended in pregnancy because it is claimed to significantly reduce the severity and outcomes of disease in newborns.

• But parents and healthcare educators should be aware that Tdap does not guarantee prevention of carriage or transmission.

Tdap’s limitations remain:

It does not protect from infection or transmission & can create carriers.

This is rarely discussed in prenatal visits, raising the point:

If Tdap doesn’t prevent a mother from carrying pertussis in her airway, should families be told this upfront so they can properly protect their newborn?

And another:

If vaccinated caregivers can carry pertussis unknowingly, is the recommendation to “make sure everyone around the baby has Tdap” actually reducing risk, creating risk, or giving false reassurance?

Why This Matters So Much for Newborns

Newborns are the most vulnerable of all.

They rely entirely on the honesty, awareness, and health habits of the people around them.

But if vaccinated individuals can:

• feel fine

• show zero symptoms

• still carry pertussis in their throats

• and unknowingly transmit it…

…it opens a bigger discussion:

Should newborn protection rely solely on Tdap status, or should it rely on informed behavior and responsible boundaries?

Layered Protection Makes the Most Sense

Rather than relying on a single tool that may be aiding the problem, families benefit from a layered approach:

• Careful visitor boundaries

• Hygiene and respiratory awareness

• Honest communication among family members

• Avoiding blind trust in “but I’m vaccinated”

Because here’s the contradiction that every family deserves to understand:

If vaccination reduces symptoms but not transmission, the people most likely to spread pertussis may be the ones who don’t realize they’re carrying it.

That’s not anti-science

that’s the actual science.

What This Means for Doulas & Educators

Birth professionals have the responsibility to:

• provide nuanced education

• acknowledge contradictions

• and help families navigate real-life risk, not theoretical models

Because asking questions is not “controversial”

it’s conscientious, responsible, and necessary for informed consent.

Key questions doulas can invite families to consider:

If a vaccine doesn’t prevent transmission, how else can I protect my newborn?

Pertussis protection is not as simple as vaccination = safety.

The research clearly shows that:

Tdap does not reliably stop silent carriage or transmission.

So the real question becomes:

Why is the public told that vaccination alone protects newborns

when the science shows newborn protection requires much more than that?

Families deserve the full picture so they can create a protection plan based on truth, not assumptions, and safeguard their newborns with confidence and clarity.

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• Tdap is an acellular (non-live) vaccine — it contains purified pertussis antigens.

• Strong experimental and clinical evidence shows aP vaccines do not reliably prevent nasopharyngeal colonization or onward transmission (shown clearly in the baboon model, and supported by human carriage/challenge and epidemiology). That immunological profile is the scientific basis for the “silent carrier” hypothesis. PubMed+2PMC+2

• Mechanistic reason: aP vaccines induce systemic (serum IgG) responses but are less effective at inducing mucosal immunity (e.g., local secretory IgA and tissue-resident T cell/Th17 responses) in the upper respiratory tract that block colonization. That gap helps explain why colonization and asymptomatic infection remain possible. Nature+1

Key primary studies & reviews

Warfel JM et al., 2014 — Acellular pertussis vaccines protect against disease but fail to prevent infection and transmission in a nonhuman primate model. (PNAS)

What it shows: In the infant baboon model, animals vaccinated with acellular pertussis vaccines were protected from severe symptoms but still became colonized and transmitted Bordetella pertussis to others. This is one of the most-cited experimental demonstrations that aP can disconnect disease protection from colonization-blocking. PubMed+1

de Graaf H. et al., 2019/2020 — Controlled human infection with Bordetella pertussis induces asymptomatic, immunizing colonization. (Clinical Infectious Diseases, full text available)What it shows: A controlled human challenge demonstrated that B. pertussis can colonize the nasopharynx and induce immune responses without causing clinical pertussis symptoms — i.e., asymptomatic carriage is inducible and immunogenic in humans. This supports the plausibility of symptom-less carriage/transmission in people. PMC+1

Gill CJ et al., 2021 — Asymptomatic Bordetella pertussis infections in a longitudinal cohort (eLife)

What it shows: Using sensitive qPCR surveillance, this study documented a high incidence of B. pertussis detections that were asymptomatic, including among infants. This highlights that asymptomatic infection can occur in real-world cohorts and may be under-recognized. eLife

Alghounaim M. et al., 2022 — Whole-cell and acellular pertussis vaccine: reflections on immunity and effectiveness (systematic review / review article)

What it shows: Synthesizes evidence comparing wP and aP vaccines, emphasizing that wP tends to induce broader, longer-lasting protection that better prevents colonization in animal models; aP has advantages in reactogenicity but limitations in mucosal immunity and duration of protection. PMC

Acosta AM. et al., 2024 — Evaluation of Asymptomatic Bordetella carriage in a highly aP-vaccinated population (J Pediatric Infectious Diseases / cross-sectional study)

What it shows: Direct investigation of asymptomatic carriage in contemporary aP-vaccinated populations; found carriage may be uncommon in that sample, but concludes further study is needed. This paper demonstrates the mixed nature of human surveillance data and the need for more population-level carriage work. OUP Academic+1

Merkel & Controlled Human Infection Model commentary / reviews (2019–2020) — discuss development of human challenge models and the implications of carriage for vaccine development and epidemiology. PMC+1

Recent immunology / mechanism overviews (2024–2025) — papers and commentaries summarizing why aP vaccines elicit strong systemic IgG but weaker mucosal/Th17 responses, and why that matters for colonization and transmission. Example: Jazayeri et al., 2025 (Nature Microbiology commentary/review). Nature

Official guidance / vaccine facts (CDC, ACOG) — clarify vaccine type (acellular, non-live), safety, and continued recommendation for Tdap in pregnancy and adults because of disease prevention benefits. (Useful for contextual balance.) CDC+2CDC+2

• Systemic IgG (blood antibodies): aP/Tdap triggers serum antibody levels that neutralize pertussis toxin to attempt to limit severe symptoms.

• Mucosal immunity (upper airway): preventing colonization requires local secretory IgA and tissue-resident T cells (Th17 responses) at the nasopharyngeal mucosa. aP vaccines are poor at inducing strong mucosal IgA/Th17 compared with natural infection or some whole-cell vaccines. Without strong mucosal defenses, B. pertussis can colonize the nasopharynx even if the person doesn’t cough or show classic symptoms — hence the term “silent carriage.” Nature+1

Key Studies & Reviews on Mechanistic Immunity (Mucosal / Tissue-Resident T Cells, IgA, Th17)

Next-Generation Pertussis Vaccines Based on the Induction of Protective T Cells in the Respiratory Tract

• PubMed / review — argues that aP vaccines fail to prime respiratory tissue-resident memory T cells (Tₙₘ) and Th17 responses, which are important for mucosal immunity. PubMed

• They note that Th1 and Th17, plus secretory IgA, are especially important for long-term protection in the nasal cavity. PubMed

Suppression of mucosal Th17 memory responses by acellular pertussis vaccines enhances nasal Bordetella pertussis carriage

• PubMed / experimental in mice — shows that aP vaccines do not induce IL-17+ tissue-resident memory (Tₙₘ) CD4⁺ cells in nasal mucosa, and that these cells are crucial for clearing nasal B. pertussis. PubMed

• IL-17–deficient mice failed to clear nasal infection, indicating the importance of IL-17+ Tₙₘ in mucosal control. PubMed

Acellular Pertussis Vaccines Induce CD8+ and CD4+ Regulatory T Cells That Suppress Protective Tissue-Resident Memory CD4+ T Cells, in Part via IL-10

• PMC / mouse model — shows that aP vaccines induce regulatory T cells (Tregs) that secrete IL-10, which then suppress the development of IL-17-producing tissue-resident memory CD4+ T cells in the respiratory tract. PMC

• Blocking IL-10 signaling during or after vaccination restores some IL-17+ Tₙₘ and improves bacterial clearance in the nose. PMC

IL-17 and IFN-γ–producing Respiratory Tissue-Resident Memory CD4 T Cells Persist for Decades in Adults Immunized as Children With Whole-Cell Pertussis Vaccines

• Journal of Infectious Diseases / human tissue study — in tonsil / nasal tissue of adults, those who received whole-cell pertussis (wP) in childhood had significantly more IL-17A and IFN-γ producing tissue-resident memory CD4+ T cells compared to those who got aP as children. OUP Academic+1

• This suggests that aP priming in humans may not generate or maintain the same mucosal Tₙₘ pool as wP. OUP Academic

Pertussis Vaccines and Protective Immunity

• Review (PMC) — summarizes animal and human evidence: aP vaccination leads to strong Th2 (and IgG) responses, but weak Th1 / Th17 responses; unlike whole-cell or natural infection, aP does not drive robust mucosal T cell responses. PMC

• Also discusses that in non-human primate (baboon) models, aP vaccines don’t prevent colonization or transmission. PMC

Mucosal IgA Antibodies are Critical for Bacterial Clearance of Bordetella pertussis in the Baboon Model

• PubMed, 2025 — shows that in baboons, higher mucosal (nasopharyngeal) IgA titers correlate with better clearance of B. pertussis. PubMed

• This strongly supports the idea that mucosal IgA is functionally important, and its absence / lower induction after aP vaccination may impair clearance.

Acellular Pertussis Vaccine Inhibits Bordetella pertussis Clearance from the Nasal Mucosa of Mice

• MDPI Vaccines, mouse study — demonstrates that aP-immunized mice clear B. pertussis from the lungs but not effectively from the nasal mucosa, unlike whole-cell vaccination. MDPI

• Also shows differences in antibody breadth; whole-cell vaccine induces a broader antibody response (more antigen targets) than aP. MDPI