Adverse Events Following Immunization

Adverse Events Following Immunization - Defining & Sorting

• Definition (WHO): An AEFI is any untoward medical occurrence which follows immunization and which does not necessarily have a causal relationship with the usage of the vaccine.

• Operational Classifications of AEFI: 📌 Mnemonic: "Very Quiet Errors Anxiously Coincide"

Adverse Events Following Immunization - Mild to Wild

AEFIs range from common, mild events to rare, serious ones.

• Common Minor AEFIs:
  • Local: Pain, swelling, redness at injection site.
  • Systemic: Fever (<38.5°C), malaise, irritability, headache.
• Serious AEFIs (Rare):
  • Anaphylaxis (immediate, severe allergic reaction).
  • Hypotonic-Hyporesponsive Episode (HHE): Sudden pallor, limpness, ↓responsiveness.
  • Persistent Inconsolable Screaming: Continuous crying for ≥3 hours.
  • Seizures: Febrile or afebrile.
  • Thrombocytopenia: ↓Platelet count.
  • Guillain-Barré Syndrome (GBS): Ascending paralysis.
  • Encephalopathy: Altered mental status.
  • Vaccine-Associated Paralytic Poliomyelitis (VAPP): With OPV.
  • BCG-osis (Disseminated BCG infection): In immunocompromised.
  • Sepsis, Toxic Shock Syndrome (TSS).

Adverse Events Following Immunization - Report & Respond

• AEFI Surveillance (India):
  • Objectives: Detect, manage, assess causality, maintain trust in immunization programs.
  • Reporting: Health workers (ANM, ASHA, MO) report to District Immunization Officer (DIO). Serious AEFIs (death, disability, hospitalization, cluster) must be reported via Standard AEFI Reporting Form within 24 hours.
• Investigation: Serious AEFIs are investigated by the DIO/designated team to determine the cause and guide corrective actions.
• Anaphylaxis Management:
  • Recognize: Rapid onset, multi-system signs (e.g., respiratory distress, ↓BP, skin/mucosal changes). 📌 Use ABCDE (Airway, Breathing, Circulation, Disability, Exposure) approach.
  • Action: Call for help. Administer IM Adrenaline (anterolateral thigh): $0.01 \text{ mg/kg}$ (or $0.1 \text{ mL/10kg}$) of 1:1000 solution (max $0.5 \text{ mg}$). Repeat every 5-15 minutes if needed (up to 3 doses).
• Febrile Seizures Management:
  • Usually benign and self-limiting. Manage fever with antipyretics (e.g., paracetamol). Provide reassurance. Refer if seizure is prolonged (>15 min) or recurrent.

⭐ Intramuscular adrenaline is the first-line treatment for anaphylaxis following immunization and should be administered promptly.

Flowchart: AEFI Reporting Pathway in India

Adverse Events Following Immunization - Cause or Coincidence?

• Purpose: Crucial to determine if an AEFI is truly vaccine-caused or coincidental, guiding public health response and maintaining trust.
• Key Factors in Assessment:
  • Temporal relationship
  • Biological plausibility
  • Strength of association
  • Consistency of evidence
  • Specificity of event
• WHO AEFI Causality Categories:
  • A: Consistent causal association with immunization
  • B1/B2: Indeterminate (e.g., conflicting data, new signal)
  • C: Inconsistent with causal association (Coincidental)
  • D: Unclassifiable (insufficient data)

⭐ Causality assessment helps differentiate events truly caused by a vaccine from coincidental events, which is vital for vaccine safety communication.

High-Yield Points - ⚡ Biggest Takeaways

• AEFI is any untoward medical occurrence post-immunization, not necessarily causal.
• AEFI types: Vaccine product/quality defect, immunization error/anxiety, coincidental event.
• Most common: Minor local reactions (pain, swelling, redness) and fever.
• Serious AEFIs: Anaphylaxis (rare), febrile seizures, thrombocytopenia, GBS, encephalopathy.
• Anaphylaxis management: Epinephrine (Adrenaline) is the first-line treatment.
• Programmatic errors (e.g., wrong route, unsterile technique) are preventable causes of AEFIs.
• Prompt AEFI reporting and causality assessment are crucial for pharmacovigilance.