Localized Reaction to Flu Shot
Symptoms
Localized reactions to influenza vaccine are common, affecting 10-64% of patients, and consist primarily of soreness, pain, redness, and swelling at the injection site that typically lasts less than 2 days. 1
- Pain at the injection site is the most frequent symptom, occurring in 10-64% of vaccinated adults and resolving within 2 days 1
- Redness and swelling at the injection site are also common manifestations 2
- In children with asthma aged 9 months-18 years, 20-28% experience local pain and swelling 1
- Among children aged 6 months-4 years with chronic conditions, approximately 23% develop local reactions 1
Important Context
- These reactions are inflammatory, not infectious - the vaccine contains only noninfectious killed viruses and cannot cause influenza 1, 2
- Local reactions typically are mild and rarely interfere with daily activities 1
- Symptoms beginning 6-12 hours post-vaccination and lasting 1-2 days represent normal vaccine response, not allergy 3
Treatment Approach
Apply cold compresses to the injection site and use acetaminophen for symptomatic relief, as these reactions resolve spontaneously within 2-3 days without specific treatment. 2
Immediate Management
- Apply cold compresses to reduce pain and swelling at the injection site 2
- Rest the affected arm but maintain gentle movement to prevent stiffness 2
- Avoid pressure or excessive use of the affected arm for 24-48 hours 2
- Acetaminophen can be used for pain management and comfort 4
When to Seek Medical Attention
- Local reaction persisting beyond 2-3 days warrants medical evaluation 2
- Severe swelling, increasing pain, or signs of infection (increasing warmth, redness extending beyond injection site, purulent discharge) require immediate assessment 2
- Systemic symptoms such as high fever, significant malaise, or allergic reactions (hives, angioedema, respiratory distress) need urgent medical attention 2, 3
Critical Pitfalls to Avoid
- Do not mistake normal local reactions for infection - these are inflammatory responses, not infectious processes, and antibiotics are not indicated 2
- Do not confuse local reactions with true allergic reactions - true IgE-mediated allergic reactions occur within minutes to 4 hours and present with hives, angioedema, or anaphylaxis, not isolated injection site soreness 3
- Do not attribute coincidental respiratory illness occurring days after vaccination to the vaccine itself, as the inactivated vaccine cannot cause influenza 1, 2
- Avoid using antibiotics for local reactions, which are inflammatory rather than infectious 2
Special Considerations
Extensive Limb Swelling
- Extensive limb swelling can occur, particularly after multiple doses of vaccines, and is more common when deltoid injection is used in children under 3 years 5
- These reactions resolve with symptomatic treatment and do not contraindicate future vaccination 5
Rare Arthus Reaction
- Arthus reaction (type III hypersensitivity) is rare and characterized by severe pain, swelling, induration, and edema, occasionally with necrosis or ulceration 6
- Most mild cases resolve without treatment; severe cases may require anti-allergy treatment 6
- This reaction typically occurs after repeated vaccinations due to pre-existing antibodies 6