What are the potential adverse effects following immunization?

Adverse Effects Following Immunization

Adverse effects following immunization are classified into three main categories: local reactions (most common and least severe), systemic reactions (less frequent), and allergic reactions (most severe but rarest), with the vast majority being mild and self-limited. 1

Classification Framework

The Advisory Committee on Immunization Practices (ACIP) categorizes adverse events following immunization into four distinct types 1:

1. Vaccine-Induced Events

• These are caused by the intrinsic characteristics of the vaccine and the individual's immune response 1
• Would not have occurred without vaccination 1
• Example: vaccine-associated paralytic poliomyelitis 1

2. Vaccine-Potentiated Events

• Events that would have occurred anyway but were precipitated by vaccination 1
• Example: first febrile seizure in a predisposed child 1

3. Programmatic Errors

• Caused by technical errors in vaccine preparation, handling, or administration 1
• These are preventable through proper technique and protocols 1

4. Coincidental Events

• Temporally associated with vaccination by chance or caused by underlying illness 1
• Not causally related to the vaccine itself 1

Clinical Presentation by Severity

Local Reactions (Most Common)

• Injection site manifestations: tenderness, pain, soreness, redness, and swelling 1, 2, 3
• Occur in the majority of vaccine recipients 2
• Usually the least severe category 1
• Important: Local soreness, redness, or swelling with temperature <40.5°C (105°F) are NOT contraindications to future vaccination 2

Systemic Reactions (Less Frequent)

• Fever: reported in 2.4%–6.5% of Tdap recipients 2
• Constitutional symptoms: fatigue (92.9%), malaise (83.8%), headache, weakness 1, 3
• Neurological: dizziness, tremor, restlessness 4
• Gastrointestinal: nausea and vomiting 4
• Occur less frequently than local reactions 1

Allergic Reactions (Most Severe, Rarest)

• Anaphylaxis: the most severe but least frequent adverse event 1
• Usually begins within minutes of vaccine administration 1
• Severe allergic reactions after vaccination are rare 1
• Requires immediate recognition and treatment with epinephrine 1

Specific Serious Adverse Events

Guillain-Barré Syndrome (GBS)

• Tetanus-toxoid-containing vaccines can trigger GBS in adults, but this is exceedingly rare 2
• Risk is extremely low: only 1 case reported when 2 cases were expected by chance in 1.2 million doses 2
• Persons with history of GBS within 6 weeks of receiving tetanus toxoid may be at increased risk for recurrence 2

Brachial Neuritis

• Associated with tetanus vaccination 2
• Relative risk of 5-10 compared to background incidence 2

Syncope (Vasovagal Reaction)

• Can occur after vaccination, most commonly among adolescents and young adults 1
• 40% of reported episodes occur among persons aged 10-18 years 1
• 63% of syncopal episodes occur <5 minutes after vaccination, and 89% occur within 15 minutes 1
• Critical: Can result in serious injury including skull fractures and cerebral bleeding from falls 1
• Approximately 12% of reported syncopal episodes resulted in hospitalization 1

Critical Clinical Pitfalls to Avoid

Do NOT Delay Vaccination For:

• Mild respiratory illness with or without fever 1
• Minor local reactions (soreness, redness, swelling) 2
• Fever <40.5°C (105°F) 2

Avoid Unnecessary Boosters:

• Increases risk of Arthus-type (immune complex) reactions 2, 5
• Patients with prior Arthus reactions should not receive tetanus toxoid until >10 years after the most recent dose, even for contaminated wounds 2

Proper Administration Technique:

• Accidental injection into digits, hands, or feet may result in loss of blood flow to the affected area 4
• Injection into the buttock has resulted in cases of gas gangrene 4
• Rare cases of necrotizing fasciitis and myonecrosis have been reported following epinephrine injection in the thigh 4

Post-Vaccination Observation

Vaccination specialists recommend observing persons for 15-20 minutes after vaccination when possible 1:

• This allows for immediate recognition and treatment of anaphylaxis 1
• Enables management of syncope before injury occurs 1
• All vaccine providers should have epinephrine and airway equipment immediately available 1
• All providers should be certified in cardiopulmonary resuscitation 1

Reporting Requirements

• Healthcare providers are required to report selected events to the Vaccine Adverse Event Reporting System (VAERS) 1
• Serious or unusual adverse events should be reported regardless of whether the provider thinks they are causally associated 1
• Reporting is essential to document low risks and identify programmatic errors for corrective action 6