A woman's breasts ballooned in size after getting her Covid vaccine in a first-of-its-kind case.
The 19-year-old from Canada went from a B cup to triple G cup within six months after receiving the two-shot course.
She received her first dose of the Pfizer Covid vaccine in September 2022 and her breasts started tingling and growing slightly.
Both of these effects then worsened after she received her second dose of the vaccine about three weeks later.
She finally went to doctors at six months when her breasts grew to such an extreme size. For comparison, the average American woman's cup size is DD.
Doctors treating the woman suggested her Covid vaccine may have triggered pseudoangiomatous stromal hyperplasia (PASH), an overgrowth of cells that usually causes benign lumps in the breasts and has only ever been seen in around 200 patients.
This is the first-ever case linking PASH to a vaccine, though the experts cautioned that it cannot be proven to be the culprit.
It's unclear exactly how the vaccine may have triggered the growth, but some case studies have suggested Covid vaccines may trigger an immune response leading to temporarily swollen lymph nodes, which makes breasts seem larger.
The experts, from the University of Toronto, wrote in a medical journal last month: 'This case is the first to demonstrate a temporal association between PASH-associated gigantomastia and a vaccine.'
Experts have also noted that adverse reactions to Covid vaccines are extremely rare, and the benefits of getting the shot outweigh potential complications.
Serious side effects impact around one in 200,000 people, according to official US data.
CDC data also shows only two serious adverse effects have been well established after Covid vaccination - anaphylaxis and myocarditis or pericarditis, two types of heart damage.
The woman in the case study had no underlying conditions. While her breasts seemed swollen and saggy, there were no masses.
An ultrasound and CT scan slightly swollen lymph nodes around the woman's armpits and dense blood vessels, which they believe was from the enlarged breast tissue.
PASH is a benign breast condition found in less than 200 people worldwide since it was first described in 1986.
It normally causes non-cancerous lesions breast lumps made from cells called myofibroblasts.
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