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"COVID Arm": We Asked A Doctor About The Unusual But Harmless Delayed Reaction


Rachael Funnell

Social Editor and Staff Writer

clockJun 22 2021, 17:28 UTC
COVID Arm: An Unusual But Harmless Side Effect From The COVID-19 Vaccine

"COVID arm" presents with a red lump at the vaccine's injection site around a week after the jab was given. Image courtesy of Dr Kimberley Blumenthal, Massachusetts General Hospital

It’s possible to love vaccines without actually loving the process of receiving one. It’s not often in life that we offer ourselves up to be pricked with a needle and the fact that it’s sort of like a dress rehearsal for a disease means it’s perfectly normal to feel a bit rubbish afterward. However, the small risks are worth it for the protection it gives to not just ourselves but those around us, too.

While the COVID-19 vaccines were pushed through in a record-breaking time frame (thanks to a unified, global effort), like all medicines they too underwent the stringent and extensive trial phases to ensure both their efficacy and safety. That they passed, however, doesn’t mean that there won’t be side effects (real or imagined), as when giving out any medication on a global scale you are pretty much guaranteed to run into complications; big or small, rare or common.


A small but unusual side effect that is beginning to emerge as further vaccines roll out has been dubbed “COVID arm” and, while it’s considered to be harmless, it’s an unusual one. Most people will experience some degree of discomfort in the days following their vaccination, but COVID arm doesn’t kick in until a week after the jab.

Associated with the mRNA-1273 vaccination – more commonly known as Moderna – the side effect is known to those who have described it as a delayed cutaneous reaction, or delayed localized hypersensitivity reactions. Those who experience it find their arm is symptomless for around a week following their vaccination only to wake up one morning and find an uncomfortable blob over the injection site that can be red and quite large. The blob might also be painful, itchy, and hot and may linger for a few days.

covid arm
The lesion can be itchy and warm. Image courtesy of Dr Kimberley Blumenthal, Massachusetts General Hospital

Correspondence published in the New England Journal of Medicine has warned that, given COVID arm’s rarity, health care workers might not know what they’re dealing with – which can lead to the unnecessary prescribing of antibiotics in some cases. Appropriate treatment for the condition is a simple case of dealing with the symptoms, as the reaction should go away by itself within a few days.


“If there is pain, taking acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) can help,” said Dr Kimberley Blumenthal of Massachusetts General Hospital and Harvard Medical School to IFLScience. “If there is a localized rash, topical corticosteroids can help. If there is localized swelling, ice can help. If there is itching and rash, then we often recommend non-sedating antihistamines such as cetirizine (Zyrtec) or fexofenadine (Allegra).”

Its rarity means that the onset of COVID arm remains relatively understudied, but several papers in the New England Journal of Medicine report on the small number of cases that have come to light – including this series of 12 patients, and this case series in vaccine recipients who are Black, Indigenous, or People of Color.

Fortunately, even if you experience COVID arm, the delayed reaction isn’t considered to be a reason not to get the second jab. Furthermore, research has found that not everyone who experiences COVID arm following the first vaccine will have it again for the second jab. Reports of COVID arm remain relatively low, though it could be that for some the symptoms are so mild as to not be considered worth reporting. If it does happen to you, however, you can lend a hand to vaccination research by letting the relevant people know.

covid arm
The hypersensitivity reaction can look scary but is believed to be safe. Image courtesy of Dr. Kimberly Blumenthal, Massachusetts General Hospital

“Anyone experiencing such a reaction should report their case to the CDC's Vaccine Adverse Event Reporting System. Reactions can also be reported directly to the vaccine manufacturer (e.g., Moderna),” continued Blumenthal. “We would also appreciate it if they can add their reaction details to our research registry, which is linked on this website.”

COVID arms sufferers from the United Kingdom can contact the Medicines and Healthcare products Regulatory Agency to report side effects, but for anything that requires medical attention, you should speak with your GP.

Blumenthal and colleagues will be continuing their investigations into vaccine reactions, looking at their prevalence across diverse geographic regions, communities, and vaccine manufacturers to gain a better understanding as to who is at risk for cutaneous reactions and their clinical implications.




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