Immunology · Year 2 · from Immunology

Case 1: Vaccine-Preventable Disease in Unvaccinated Child

Patient Presentation

Demographics: 4-year-old male

Chief Complaint: High fever and rash for 3 days

History of Present Illness: The patient developed high fever (40C) 3 days ago followed by cough, coryza (runny nose), and conjunctivitis. Yesterday a rash appeared on his face and has spread down his trunk. His mother reports he has not received any childhood vaccinations due to parental concerns about vaccine safety.

Vaccination History:

  • No vaccines received (parental exemption)

Social History:

  • Attends daycare
  • Recent outbreak of measles in community

Physical Examination:

  • Temperature: 39.8C
  • Heart rate: 130 bpm
  • General: Ill-appearing, irritable
  • Eyes: Bilateral conjunctival injection
  • Mouth: Koplik spots on buccal mucosa (white spots opposite molars)
  • Skin: Erythematous maculopapular rash beginning on face, spreading to trunk
  • Lungs: Clear
  • Lymph nodes: Cervical lymphadenopathy

Workup and Results

Laboratory Studies:

  • WBC: 3,800/mcL (leukopenia common in measles)
  • Measles IgM: Positive
  • Measles IgG: Negative
  • Measles PCR (nasopharyngeal swab): Positive

Clinical Image

Clinical photograph demonstrating characteristic measles presentation with erythematous maculopapular rash and inset showing Koplik spots on buccal mucosa - pathognomonic for measles.

Diagnosis

Measles (Rubeola) in Unvaccinated Child

Classic presentation:

  • Prodrome: Fever, cough, coryza, conjunctivitis (3 C's)
  • Koplik spots (pathognomonic)
  • Maculopapular rash spreading cephalocaudally

Discussion

This case illustrates vaccine-preventable disease:

  • Herd Immunity Threshold: The lecture describes how measles has an R0 of 12-18, requiring 92-95% population immunity for herd protection. Unvaccinated individuals are protected only when this threshold is maintained.
  • MMR Vaccine: The lecture explains that MMR is a live attenuated vaccine typically given at 12-15 months with a second dose at 4-6 years. Two doses provide 97% immunity against measles.
  • Immunological Memory: The lecture emphasizes that vaccines work by exploiting immunological memory. Memory B and T cells generated during vaccination mount rapid, robust responses upon natural exposure.
  • Live Vaccine Characteristics: Live attenuated vaccines like MMR generally require only one or two doses, induce strong cellular and humoral immunity, but are contraindicated in immunocompromised patients.

Treatment Plan

  1. Supportive Care:
  • Antipyretics for fever
  • Adequate hydration
  • Vitamin A supplementation (reduces complications and mortality)
  1. Isolation:
  • Airborne precautions (negative pressure room)
  • Contagious from 4 days before to 4 days after rash onset
  • Exclude from daycare until non-infectious
  1. Contact Tracing:
  • Notify public health department
  • Post-exposure prophylaxis for susceptible contacts
  • MMR vaccine within 72 hours or immunoglobulin within 6 days
  1. Monitoring for Complications:
  • Otitis media
  • Pneumonia (most common cause of death)
  • Encephalitis
  • SSPE (rare, late complication)
  1. Family Counseling:
  • Discuss importance of completing vaccination series after recovery
  • Address vaccine concerns with evidence-based information

Teaching Points

  1. Measles requires 92-95% population immunity for herd protection (R0 12-18)
  2. MMR vaccine provides 97% protection with two doses
  3. Live attenuated vaccines are contraindicated in immunocompromised patients
  4. Koplik spots are pathognomonic for measles
  5. Vitamin A supplementation reduces measles complications

All cases for this lecture as Markdown