Can swollen lymph nodes in the neck be a side effect of the Moderna (mRNA-1273) COVID-19 vaccine in adults?

Swollen Lymph Nodes in the Neck After COVID-19 Vaccination

Yes, swollen lymph nodes in the neck are a recognized side effect of the Moderna COVID-19 vaccine, occurring as a normal immune response when the vaccine drains to cervical and supraclavicular lymph nodes. 1

Mechanism and Expected Occurrence

Lymph node enlargement after COVID-19 vaccination is a normal immune response that occurs when locally activated antigens accumulate at the injection site and migrate to draining lymph nodes. 1 Since COVID-19 vaccines are administered intramuscularly into the deltoid muscle, vaccination-associated adenopathy typically occurs in the axilla and supraclavicular region, but can also involve cervical nodes. 1

Clinical Trial Data for Moderna Vaccine

• In the Phase 3 trial for Moderna, adenopathy was reported as an unsolicited event in 1.1% of patients. 1
• "Axillary swelling or tenderness" occurred in up to 16.0% in patients aged 18-64 years and up to 8.4% of patients over 65 years of age (compared to 4.3% and 2.5% in placebo groups). 1
• In 0.3-0.6% of patients, symptoms were severe enough to require prescription medicine for relief. 1

Timeline and Duration

The typical timeline for vaccine-associated lymphadenopathy is predictable and helps distinguish it from other causes:

• Onset: Lymph node swelling manifests within 2-4 days after either dose. 1, 2
• Clinical duration: Averages 1-2 days for Moderna (compared to 10 days for Pfizer-BioNTech). 1
• Imaging findings may persist longer: While clinical symptoms resolve quickly, imaging studies may show persistent adenopathy for weeks to months. 1, 3
• One case report documented axillary lymph node swelling remaining for up to 6 months after vaccination, though improved. 3

Location Patterns

The location of swollen lymph nodes should be ipsilateral (same side) as the vaccination site:

• Cervical, supraclavicular, infraclavicular, retroclavicular, or axillary lymph nodes can be affected. 4
• In four out of five cases in one series, adenopathy occurred ipsilaterally to the injection site. 4
• Both cervical and low neck lymphadenopathy have been documented after COVID-19 vaccination. 5, 6, 7

Clinical Assessment and Red Flags

When evaluating neck lymphadenopathy after vaccination, assess these key features:

• Timing correlation: Swelling within 2-4 days of vaccination strongly suggests vaccine-related adenopathy. 2
• Laterality: Should match the injection arm. 2, 4
• Pain characteristics: Tenderness is common with vaccine-related adenopathy. 2
• Systemic symptoms: Fever >38°C, tachycardia, or altered mental status suggest infection rather than reactive adenopathy. 2

Warning Signs Requiring Further Evaluation

• Rapidly progressive swelling beyond the expected 2-4 day timeline. 2
• Severe pain requiring prescription medication (though this occurred in 0.3-0.6% of vaccine recipients). 1, 2
• Persistent symptoms beyond 2 weeks warrant imaging evaluation. 2
• Fever or systemic toxicity suggesting infection. 2

Management Approach

For typical vaccine-associated adenopathy presenting within 2-4 days of vaccination, reassurance and observation are appropriate without imaging. 2

Algorithm for Management

1. Low-risk patients (no cancer history, typical timeline, ipsilateral to injection): Expectant management without default follow-up imaging. 1

2. Higher-risk patients (cancer history, particularly breast, head/neck, lymphoma, melanoma): Short-interval follow-up imaging with ultrasound at least 6 weeks later may be obtained. 1

3. Persistent adenopathy beyond 10-14 days: Ultrasound is the initial imaging modality. 2

4. High nodal metastatic risk requiring immediate confirmation: Tissue biopsy should be considered when immediate histopathologic confirmation is necessary for timely patient management. 1

Critical Pitfall: Cancer Patients

In patients with cancer history or undergoing cancer surveillance, vaccine-associated adenopathy can mimic metastatic disease, leading to unnecessary biopsies or treatment changes. 1 This is particularly relevant for:

• Breast cancer 1
• Head and neck cancers 1
• Lymphoma 1
• Melanoma of upper extremities 1

Prevention Strategies for Cancer Patients

• Schedule routine imaging (screening, surveillance) either before vaccination or at least 6 weeks after the final vaccination dose to allow reactive adenopathy to resolve. 1
• Administer the vaccine on the side contralateral to the primary or suspected cancer. 1
• Both vaccine doses should be administered in the same arm. 1
• Do not delay clinically indicated imaging (acute symptoms, treatment monitoring, urgent treatment planning) due to prior vaccination. 1

Documentation Requirements

Vaccination information must be systematically collected and communicated:

• Date(s) administered 1
• Injection site(s) and laterality 1
• Type of vaccine 1
• This information should be included in every pre-imaging patient questionnaire and made readily available to interpreting radiologists. 1

Patient Education

Patients should be informed that lymph node swelling is an expected immune response as the body develops antibodies to vaccination. 1 For patients with cancer concerns or upcoming imaging, they should be advised to schedule routine examinations either before or at least 6 weeks after completion of vaccination to reduce the need for additional testing. 1