#191: Vaccine Preventable Illnesses, TWO

September 9, 2026 | By Brian Ward

Audio

Vaccine preventable illnesses have been on the run since the first smallpox vaccine was administered in 1789, however recent trends in vaccine uptake has led to resurgence of these infectious diseases. Today, each pediatrician must be able to recognize and combat pathogens like Bordetella pertussis, Strep pneumonia, and Haemophilus influenzae.

Vaccine Preventable Illnesses Pearls

1. Pertussis is typically an afebrile illness, though the cough can last weeks to months!
2. Neither wild type infection nor vaccine elicits life long pertussis immunity.
3. Pediatric pneumococcal vaccination has reduced penicillin resistance because fewer children carry pneumococci in the nasopharynx.
4. The Hib vaccine brought incidence of Hib from meningitis from roughly 10,000 cases/year to 20–30 cases/year in the US, on par with shark attack incidence.
5. Hib is the Maryl Streep of illnesses; it can do anything!

Vaccine Preventable Illnesses, TWO 

Pertussis (Whooping Cough)

Presentation

Pertussis classically follows a symptomatic pattern, though in vaccinated patients, these phases may blend together:

• Catarrhal phase (runny nose phase)- less pronounced/quicker in infants. THIS is where antibiotics may modify the course
• Paroxysmal phase- the “whoop” phase
• Convalescent phase- the long-lasting cough

Pertussis typically does not present with other URI symptoms and is often an affable illness.

In high risk patients, such as infants, the runny nose phase lasts only a few days and they may not have the typical “whoop”.  Infants also present with apnea.

Rates decreased with vaccines, but that’s not the whole story

• Pre-Vaccine era, the United States saw 250k-300k cases a year. 

• Whole cell vaccine (1940s-1990s) decreased rates to about 1,000 cases a year. 
• Now with the acellular vaccine, there is a modest increase to 25k-40k cases a year.

Whole cell was used from the 1940s to the 1990s/early 2000s and exposed the body to about 3,000 antigens, however due to concern for side effects, this was replaced by the acellular pertussis vaccine, which exposes the body to about 3-5 antigens. “Acellular”  is the “a” in DTaP and TDaP. Currently, the acellular vaccine is used.

Vaccine efficacy

Neither pertussis vaccine nor wild type pertussis infection produce lifelong immunity. This explains why we vaccinate during pregnancy. Boosters in childhood improve immunogenicity of the acellular vaccine. Current vaccine is 75-90% protective initially, however may drop to about 25% by the time children are due to TDaP (10-11yrs)

Vaccines are given to pregnant mothers to pass humoral immunity via the placenta, protecting infants.

Diagnosis:

Nasopharyngeal PCR is both ubiquitous and the gold standard. Sensitivity may wane at the tail end of the illness. Note: Bordetella parapertussis and other Bordetella infections may be caught on PCR and should be treated like Bordetella pertussis. 

Mortality

Infants are at highest risk of mortality with fatality rates of up to 1.6% in infants younger than 2 months. Risks for mortality include:

• Pulmonary hypertension
• Leukocytosis/Leukomoid reaction, sometimes requiring even plasmapheresis
• Stroke

Treatment:

Azithromycin (the famous Z-pack)

• 10mg/kg x5 days for 0-6mo
• Older children: 10mg/kg day 1, 5mg/kg days 2-5

Once children are in the coughing (paroxysmal) phase, antibiotics will likely not alter the symptom course, but it will eliminate further spread. Any household contact (including fully vaccinated individuals) should obtain post-exposure prophylaxis.

Trimethoprim-sulfamethoxazole, fluoroquinolones, and other macrolides will cover Brodetella pertussis, similar to other atypical bacterial infections.

Pneumococcus (Streptococcus pneumoniae)

Common Presentations

• Most common: otitis media, sinusitis, and non-invasive respiratory infections.
• Can cause pneumonia, though viruses account for most pediatric CAP and Mycoplasma may be more common than pneumococcus in some studies.
• Important invasive syndromes: bacteremia, meningitis, osteomyelitis, septic arthritis, and empyema (a setting where the organism is often cultured).

Vaccines and Serotypes

• PCV7 → PCV13 → PCV20 expanded serotype coverage.
• Overall invasive pneumococcal disease has declined substantially, including meningitis and bacteremia, with evidence of herd effects in adults after pediatric vaccination.
• Non-vaccine serotypes become relatively more prominent, something called serotype replacement
• Current conjugate vaccines simply cannot add unlimited serotypes due to immunologic and manufacturing constraints.
• Future direction: serotype-agnostic vaccines targeting shared pneumococcal antigens, but these remain investigational.

Diagnostic approach

• Diagnosis is usually clinical unless you have a specimen to culture (blood, CSF, pleural fluid, synovial fluid, etc.) and does not need routine PCR/serologies
• For a stable child with viral URI features, vaccination status alone should not trigger empiric antibiotics; common viral illnesses remain common. Consider pneumococcus more strongly when the child has an unusual or invasive presentation (meningitis, bacteremia, empyema, bone/joint infection).

Antibiotic Pearls

• Otitis media: Ampicillin/amoxicillin (follow standard guidelines)
• CAP: Ampicillin/amoxicillin may still be appropriate where local susceptibility supports it
• Meningitis: Ceftriaxone + vancomycin initially to cover rare ceftriaxone-resistant pneumococcus; de-escalate cautiously
• Bone/joint infection: Initial therapy often targets S. aureus and GAS (e.g., cefazolin/clindamycin depending on local practice); adjust if cultures identify pneumococcus

Interesting secondary effect: pediatric pneumococcal vaccination has been associated with reduced penicillin resistance pressure because fewer children carry vaccine-type pneumococci in the nasopharynx.

Haemophilus influenzae type b (Hib)

Historical HiB

• Pre-vaccine era: about 1 in 200 children developed invasive Hib disease.
• Roughly 10,000 cases/year of Hib meningitis occurred in the U.S. before vaccination (for context, about 20,000 children are admitted a year with the influenza virus).
• Post-vaccine: invasive Hib fell to roughly 20–30 cases/year, illustrating one of the largest vaccine success stories in pediatrics.

Presentation:

• Meningitis (the classic feared presentation).
• Epiglottitis (a medical emergency)
• Osteomyelitis and septic arthritis (once more common than Staph aureus).
• Pneumonia, bacteremia, conjunctivitis, otitis media.
• A weird characteristic violaceous facial/orbital cellulitis pattern described in older literature.

Typing: Hib vs non-typeable H. influenzae

• HiB is the encapsulated strain with Type B capsular antigen.
• Non-type B strains (A, C, D, E, F) = encapsulated, but different capsule antigens.
• Non-typeable (untypeable) strains = no capsule → no capsule antigen to type.

The vaccine targets the Type B capsule because that strain historically caused the overwhelming majority of severe pediatric invasive disease; other types are far less common.

Clinical clues in the Current Era

• Peak Hib age historically: ~6–18 months.
• In an unimmunized/under-immunized infant/toddler with meningitis, epiglottitis, bacteremia, or septic arthritis, think Hib.
• The speakers’ recent local cases were all in unvaccinated children; they emphasized this reflects lack of vaccination rather than vaccine waning.
• Routine catch-up schedules stop Hib after age 5 for most healthy children because invasive Hib becomes very uncommon beyond that age.

Treatment 

• Ceftriaxone is the empiric workhorse for invasive Hib disease (meningitis, bacteremia, epiglottitis, septic arthritis, etc.). H. influenzae can produce beta-lactamase that ineffectively hydrolyzes ceftriaxone, making ceftriaxone a better first line than ampicillin/amoxicillin. 

Immunization status is a “fifth vital sign”

When a child is unimmunized or under-immunized, widen the differential: pertussis, measles, Hib epiglottitis/meningitis, invasive pneumococcus, etc.

Use your resources (like the Red Book and the CHOP Vaccine Education Center) and consult ID when the illness pattern is unfamiliar or high risk.

And if you’ve made it this far, here is Walter’s paper on outbreaks as portrayed in cinema!

Goal

Listeners will identify and treat Bordetella pertussis, Strep pneumo, and Haemophilus influenzae infections in the unvaccinated or undervaccinated child.

Learning Objectives

After listening to this episode listeners will…  

1. Recognize patients at highest risk for pertussis infection
2. Describe the benefits and limitations of pneumococcal vaccinations
3. Recount the changing landscape of Hib infections including its prior presentations
4. Be familiar with treatment of Bordetella pertussis, Strep pneumonia, and Hemophilus influenzae infections

Disclosures

Dr Dehority reports no relevant financial disclosures. The Cribsiders report no relevant financial disclosures. 

Citation

Ward B, Dehority W, Chiu C, Masur S. “#191 Vaccine Preventable Illnesses, TWO”. The Cribsiders Podcast. http://www.thecribsiders.com/ September 9th, 2025.