Differences between the vaccines?
The frequency with which axillary adenopathy occurs as a side effect differs with the two COVID-19 vaccines, according to reports from the Centers for Disease Control and Prevention.
For the Moderna vaccine, axillary adenopathy ipsilateral to the vaccination arm was the second most frequently reported local reaction, with 11.6% of recipients aged 18-64 years reporting it after the first dose, and 16.0% reporting it after the second. The average duration of this adenopathy was 1-2 days.
For the Pfizer-BioNTech COVID-19 vaccine, the CDC notes that reports of adenopathy were imbalanced between the vaccine and placebo groups and concluded that adenopathy was plausibly related to the vaccine.
The average duration of adenopathy was approximately 10 days.
Adenopathy was reported within 2-4 days after vaccination for both vaccine groups, the CDC noted.
However, details from the cases reported by Dr. Dodelzon and colleagues paint a somewhat different picture. For example, in case 1, the patient self-detected unilateral axillary adenopathy 9 days after receiving the first dose of the Pfizer-BioNTech vaccine. In case 3, the time between receiving the Moderna vaccine and detection of adenopathy was 13 days.
In both of these cases, the time was much longer than the average duration of 1-2 days noted by the CDC. The authors suggest that in taking the patient’s vaccination history, radiologists understand that the side effect may occur up to several weeks following the COVID-19 vaccination.
In cases 2 and 4, the axillary adenopathy was incidentally noted during mammography, so it is unclear when the onset of this reaction occurred after receiving the COVID-19 vaccine.
The authors and Dr. Leung have disclosed no relevant financial relationships.
A version of this article first appeared on Medscape.com.