Definition
- Any untoward medical occurrence following immunization.
- Does not necessarily need causal relationship with vaccine usage.
- Manifests as unfavorable or unintended sign, symptom, disease, or abnormal laboratory finding.
Classification Based On Cause
| Cause Category | Pathophysiology | Clinical Examples |
|---|
| Vaccine Product-Related | Individual immune response or microbial replication due to inherent vaccine properties. | Anaphylaxis following measles vaccine; Bacillus Calmette-Guérin (BCG) adenitis. |
| Vaccine Quality Defect-Related | Manufacturing defect impacting individual response. | Incomplete viral inactivation causing abortive polio (e.g., historical Cutter incident). |
| Immunization Error-Related | Preventable errors in prescribing, preparation, handling, storage, or administration. Most common cause of serious events. | Toxic shock syndrome from contaminated measles vaccine; muscle relaxant erroneously used as BCG diluent. |
| Immunization-Triggered Stress Response | Psychological or physiological response to fear or pain of injection. Unrelated to vaccine content. | Vasovagal syncope, hyperventilation, vomiting, breath-holding spells. |
| Coincidental | Unrelated event temporally linked to vaccination by chance. | Pre-existing neurological seizure disorder manifesting post-DPT vaccination; unrelated acute gastroenteritis. |
Classification Based On Severity
Minor Events
- Common, self-limiting immune responses.
- Include local injection site pain, swelling, redness, mild fever, and irritability.
Severe Events
- Higher severity than minor reactions.
- Disabling but managed at outpatient level.
- Does not necessitate hospital admission; lacks long-term sequelae.
Serious Events
- Life-threatening occurrences.
- Require inpatient hospitalization or prolong existing hospitalization.
- Result in death, persistent or significant disability, or congenital anomaly.
- Require intervention to prevent permanent impairment.
- Manifest in clusters (two or more cases related in time, place, or vaccine).
| Vaccine | Specific Serious Adverse Event | Onset Timeline |
|---|
| Oral Poliovirus | Vaccine-associated paralytic poliomyelitis. | 1–6 months. |
| Measles | Thrombocytopenic purpura. | 7–30 days. |
| Measles, Mumps, Rubella | Encephalopathy or encephalitis. | <15 days. |
| Tetanus | Brachial neuritis. | <28 days. |
| Rotavirus | Intussusception. | <30 days. |
Classification Based On Frequency
| Frequency Category | Incidence Rate | Percentage |
|---|
| Very Common | ≥1/10 | ≥10%. |
| Common | ≥1/100 and <1/10 | 1–10%. |
| Uncommon | ≥1/1,000 and <1/100 | 0.1–1%. |
| Rare | ≥1/10,000 and <1/1,000 | 0.01–0.1%. |
| Very Rare | <1/10,000 | <0.01%. |
Surveillance And Reporting Mechanisms
- Reserved for serious and severe events.
- Notify District Immunization Officer (DIO) immediately.
- Complete Case Reporting Form (CRF) within 24 hours of notification.
- Enter case details into SAFE-VAC web portal (or Co-WIN SAFE-VAC).
Routine Reporting
- Reserved for minor and common events.
- Maintain weekly register at primary health centers, private clinics, and hospitals.
- Submit Monthly Progress Reports (MPR) through Health Management Information System (HMIS).
Investigation Protocol And Timelines
Field Investigation
- Treat serious events as medical emergencies.
- Initiate immediate field investigation for reported deaths or clusters.
- Complete Case Investigation Form (CIF) within 21 days of notification.
- State committee finalizes investigation report within 100 days.
Autopsy Guidelines
- Perform postmortem within 72 hours at medical college or district hospital.
- Send viscera for histopathological and toxicological examination; utilize videography.
- Conduct mandatory focused verbal autopsy by trained medical officer for all deaths, regardless of postmortem status.
Causality Assessment Framework
Step 1: Eligibility
- Determine if reported case satisfies minimum criteria required for causality evaluation.
Step 2: Checklist
- Review available information systematically.
- Identify evidence supporting alternative etiologies.
- Ascertain known biological plausibility or published literature linking vaccine to event.
- Evaluate strong evidence against causal association.
Step 3: Algorithm
- Apply checklist data to standardized algorithm.
- Determine trend: consistent, inconsistent, indeterminate, or unclassifiable.
Step 4: Classification
- Category A: Consistent causal association to immunization (vaccine product, quality defect, or error-related).
- Category B: Indeterminate (temporal relationship exists, but insufficient definitive evidence).
- Category C: Inconsistent causal association (coincidental underlying condition).
- Unclassifiable: Requires additional information for categorization.
Emergency Management Of Severe Anaphylaxis
Initial Resuscitation
- Place patient in recumbent position; elevate legs if tolerated.
- Administer intramuscular epinephrine (1:1,000 solution) 0.01 mL/kg/dose (maximum 0.5 mL) in anterolateral thigh immediately.
- Repeat epinephrine dose after 3–5 minutes if required.
Supportive Therapy
- Ensure airway maintenance; provide high-flow oxygen.
- Establish wide-bore intravenous access.
- Administer intravenous normal saline 20 mL/kg under pressure over 1–2 minutes for hypotension.
- Consider oral antihistamines for cutaneous symptoms (intravenous antihistamines not recommended).
- Transfer stabilized patient to emergency facility for continuous evaluation.
