What is the likely cause and management of swelling and pain traveling down the arm in an adult over 50 years old, 24 hours after receiving the Shingrix (zoster vaccine live) vaccine?

Likely Diagnosis: Normal Post-Vaccination Reaction

This is almost certainly a normal inflammatory response to Shingrix vaccination, not a complication requiring medical intervention. The swelling at the injection site with pain radiating down the arm occurring 24 hours post-vaccination represents an expected "robust take" reaction that occurs in up to 16% of vaccinees and typically resolves spontaneously within 24-72 hours 1, 2.

Understanding the Clinical Picture

Key distinguishing features of normal reactions:

• Timing: Symptoms beginning within 24 hours post-vaccination are characteristic of normal inflammatory responses, not complications 3, 2
• Pain characteristics: Pain traveling down the arm suggests local inflammation affecting surrounding tissues, which is a recognized normal variant 2
• Expected frequency: Shingrix causes injection-site reactions (pain, redness, swelling) in the majority of recipients, with 9.5% experiencing grade 3 (severe) injection site reactions compared to 0.4% with placebo 3
• Systemic symptoms: Systemic symptoms occur in 11.4% of Shingrix recipients versus 2.4% in placebo recipients 3

What This Is NOT

This presentation does NOT suggest:

• SIRVA (Shoulder Injury Related to Vaccine Administration): While SIRVA can occur with improper injection technique causing subacromial-subdeltoid bursitis 4, the 24-hour timeframe and expected resolution pattern argue against this diagnosis
• Bacterial superinfection: Secondary infections are uncommon (0.55 per 10,000 vaccinees) and typically occur within 5 days or beyond 30 days, with progressively worsening symptoms rather than the expected improvement pattern 1, 2
• VITT (Vaccine-Induced Immune Thrombocytopenia and Thrombosis): This COVID-19 vaccine complication occurs 5-30 days post-vaccination, not within 24 hours 1

Management Algorithm

Immediate management (first 72 hours):

1. Reassurance: Explain this is an expected reaction that will resolve spontaneously 2
2. Supportive care only:
   • Rest the affected arm 2
   • Oral non-aspirin analgesics (acetaminophen or ibuprofen) for pain 2
   • Oral antipruritic agents if itching develops 2
3. What NOT to do:
   • Do NOT apply topical steroids, antibacterial ointments, or any creams to the vaccination site 2
   • Do NOT prescribe empiric antibiotics 1
   • Do NOT manipulate or frequently touch the injection site 2

Monitoring parameters:

• Expected course: Symptoms should peak at 8-10 days and improve within 24-72 hours without treatment 2
• Red flags requiring re-evaluation:
  • Symptoms progressively worsening beyond 72 hours 2
  • Development of fluctuant enlarged lymph nodes (suggests infection) 2
  • Fever persisting beyond 2-3 days 1
  • Extensive limb swelling (>10 cm diameter), though even this typically resolves spontaneously within 3-14 days 2, 5

Important Clinical Caveats

This reaction does NOT contraindicate the second Shingrix dose:

• Mild to moderate local reactions are explicitly NOT contraindications to future vaccination 2
• The patient should receive the second dose 2-6 months after the first dose as scheduled 3
• Even extensive limb swelling (occurring in only 2% of patients) does not contraindicate future vaccination 2

True contraindications are limited to:

• History of anaphylactic or anaphylactic-like reactions to the vaccine or vaccine constituent 2
• Presence of moderate or severe illness with or without fever 2

Common pitfall to avoid:

• Do NOT confuse normal robust reactions (redness, swelling, warmth, pain >7.5 cm) with bacterial cellulitis—the key distinction is that normal reactions peak at days 8-10 and improve within 24-72 hours without progression, whereas bacterial infections progressively worsen unless treated 1, 2

When to Seek Urgent Medical Attention

Instruct the patient to return immediately if:

• Symptoms worsen progressively beyond 72 hours rather than improving 2
• Development of severe headache, unexplained bruising/bleeding, shortness of breath, or persistent abdominal pain (though these would suggest VITT, which occurs 5-30 days post-vaccination, not at 24 hours) 1
• Signs of true bacterial infection: increasing warmth, purulent drainage, or systemic toxicity 1, 2