How is pertussis (whooping cough) treated in a vaccinated child?

Treatment of Pertussis in Vaccinated Children

Treat this vaccinated child with azithromycin (10 mg/kg on day 1, then 5 mg/kg daily for 4 days) and isolate for 5 days from treatment start—yes, vaccinated children can still get pertussis due to waning immunity that begins 5-10 years after vaccination. 1, 2

Can Vaccinated Children Get Pertussis?

Yes, breakthrough infections occur despite full vaccination. The key points are:

• Vaccination reduces but does not eliminate infection risk. Immunity wanes 5-10 years after the last vaccine dose, making previously protected children susceptible again 3, 1, 2
• Neither vaccination nor natural disease confers lifelong immunity against pertussis or reinfection 3, 2
• Vaccinated children experience milder disease with approximately 50% reduction in duration and severity compared to unvaccinated children, though they remain contagious 1
• Clinical presentation is often atypical in vaccinated children—the characteristic "whoop" may be absent and symptoms less severe, which can delay diagnosis 1, 2

First-Line Antibiotic Treatment

Azithromycin is the preferred macrolide antibiotic for treating pertussis in children: 3, 1, 4

• Dosing: 10 mg/kg (maximum 500 mg) on day 1, then 5 mg/kg (maximum 250 mg) daily for days 2-5 1, 4
• Advantages: Better tolerability, shorter treatment duration, and superior compliance compared to erythromycin 3, 5

Alternative macrolide options include:

• Clarithromycin: 7.5 mg/kg (maximum 500 mg) twice daily for 7 days 4
• Erythromycin: 40-50 mg/kg/day divided doses for 14 days (if other macrolides unavailable) 3, 6

For macrolide allergy or intolerance:

• Trimethoprim-sulfamethoxazole for children >2 months old 3, 7

Timing and Goals of Antibiotic Therapy

The primary goal is to eradicate Bordetella pertussis from the nasopharynx and reduce transmission, not to shorten disease duration in established cases. 1

• Early treatment (catarrhal stage, first 1-2 weeks) can reduce symptom duration and severity by approximately 50% 3, 1
• Treatment during paroxysmal stage still eradicates the organism and reduces transmission, though symptom benefit is limited 3, 1
• Start antibiotics immediately when pertussis is suspected—do not delay for diagnostic confirmation 3
• 80-90% of untreated patients spontaneously clear the organism within 3-4 weeks, but remain highly contagious during this period 1, 4

Isolation Requirements

Isolate the child for 5 days after starting appropriate antibiotic treatment. 3, 1

• If antibiotics cannot be given, isolation must continue for 21 days after cough onset 1
• Respiratory droplet precautions are required during the isolation period 1
• Keep away from school, daycare, and vulnerable contacts (especially infants) during the isolation period 3

Management of Household Contacts and Close Contacts

All household and close contacts require macrolide antibiotic prophylaxis for 14 days, regardless of age and vaccination status. 1, 2

• Pertussis remains highly contagious with secondary attack rates exceeding 80% among susceptible household contacts 3, 1, 2
• Vaccinated individuals with breakthrough infections can still transmit disease to others 1
• Prophylaxis regimens are the same as treatment doses 2

Vaccination status of contacts should be verified and updated:

• Close contacts <7 years who haven't completed the 4-dose primary DTaP series should complete it with minimal intervals 2
• Those who completed primary series but haven't received pertussis vaccine within 3 years of exposure should receive a booster dose 2

Adjunctive Therapies to Avoid

Do not use β-agonists, antihistamines, corticosteroids, or pertussis immunoglobulin—these have no proven benefit in controlling coughing paroxysms or improving outcomes. 3

Monitoring for Complications

Watch for the following complications, though they are less common in vaccinated children: 1

• Common: Weight loss, sleep disturbance, post-tussive vomiting 3, 1
• Pressure-related effects: Pneumothorax, epistaxis, subconjunctival hemorrhage, rib fracture 3, 1
• Infectious complications: Secondary bacterial pneumonia, otitis media 1
• Neurologic (rare but serious): Seizures, hypoxic encephalopathy requiring immediate evaluation 1

Common Pitfalls to Avoid

• Do not dismiss pertussis based solely on vaccination status—breakthrough infections are common and should be actively considered 1
• Do not assume typical "whooping" presentation—vaccinated children often have atypical symptoms with absent whoop 1, 2
• Do not delay testing or treatment while waiting for classic symptoms to develop—early intervention reduces transmission and may shorten disease course 1
• Do not forget to treat all household contacts prophylactically—this is critical to prevent spread to vulnerable infants 1, 2