A 41-year-old female healthcare professional, monitored due to mammary cysts, with no other relevant medical background. 48 hours after receiving the second dose of the Pfizer-BioNTech COVID-19 vaccine in her left arm, she presents with an inflammatory process in her left breast, which is indurated, red and painful at the physical exploration [1,2] (Fig. 1a).
Ultrasound imaging was performed both in the acute phase and after 6 days (control). Initial findings included breast skin thickening and a poorly defined area with structural and echogenicity alterations, as well as oedema surrounding the fatty lobules and occupying the mammary parenchyma (1,2). The cysts that were previously found were also identified. No inflammatory axillary lymph nodes were identified (Fig. 1b and 1c).
The control study showed the alterations had improved greatly, and the breast almost had a normal external and radiological appearance (Fig. 2a, 2b, 2c).
The case presents a strong relationship between the inflammatory process and the history of the recent COVID-19 vaccination.
The patient had developed a COVID-19 infection in April 2020 (11 months prior), with mild symptoms such as anosmia and headaches. She did not develop serum immunity.
There have been abundant reports of adverse medical effects in those patients that had previous COVID-19 infection and subsequently are vaccinated, with various types of inflammatory responses, most notably axillar lymphadenopathy and very rarely mastitis [3,4], athough the cases described in the medical literature are related with breastfeeding,  and no medical literature has been published regarding mastitis during breastfeeding and concurrent COVID-19 infection or non-lactating mastitis after COVID-19 vaccination.
These processes are included in the inflammatory response we produce against the virus [6,7,8].
The process faded spontaneously in 6 days, only requiring anti-inflammatory and analgesic treatment.
This type of mastitis is a self-limited, aseptic inflammatory process that is immunity-mediated and therefore does not require antibiotic treatment.
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