A few hours after the injection of a dose of vaccine against the coronavirus, the arm where the injection took place can generate a little pain, as if you had a bruise. It does not matter: here is how it is explained.
The coronavirus vaccines cause some side effects. They are not serious, and their occurrence is perfectly normal since it comes from the very functioning of vaccines in general. Among the most common effects, there is a temporary state of fatigue and, even more recurrent, a slight pain in the arm affected by the bite, especially around the injection site.
This pain is similar to a cramp after intense exercise, or a big bruise. It only lasts 2-3 days in most cases and again it is mild. But where does this consequence come from?
Why do my arm hurt after the vaccine?
Pain in the arm after a vaccine injection, whether against Covid-19 or the flu, is the logical consequence of two main mechanisms:
- At the site of the injection, the bite creates a small superficial wound at the level of the muscle, which repairs itself quickly. In addition, the substance containing the vaccine must begin to circulate by diffusing gradually, which can also generate some pain when we move the muscles of the arm;
- The site of the injection represents the starting point of the immune response. This is where, for the first time, the body comes into contact with the contents of the vaccine – and in particular the “source code” of the Spike protein of the coronavirus (which is used to teach the body to fight the real virus for the day he would actually show up). It is therefore in the arm where the injection takes place that the immune system first concentrates when it launches a counterattack against what it takes for an infection. The counterattack produces local inflammation, as well as the production of white blood cells and antibodies. However, the immune response is classically at the origin, when one is sick, of various symptoms such as fever, headaches, muscle pain, fatigue, etc. In fact, after the injection of the vaccine, the injection area becomes a place particularly prone to temporary side effects such as muscle pain.
In short: when your arm hurts after injecting a dose of the vaccine, it is the result of the injection itself as well as the initiation of the immune response, which initially creates localized inflammation. This arm pain may start to occur within an hour of the injection and it lasts 2 to 3 days. You have to perceive this phenomenon in the same way as a big bruise that you could have done to yourself: it hurts in the affected area for a while, before fading.
It is also not impossible for the injection to generate redness around the injection site. If it only lasts 2-3 days, there is nothing abnormal or serious. In the case of Moderna, it is often reported that this redness can occur not just after the injection, but between 4 and 11 days after, it is “ delayed reactions “. The data on the subject show that, as long as they are temporary, this redness is nothing serious.
Another possible reaction – also reported more particularly for Moderna – and which could cause panic, but is commonplace: swelling of the glands under the armpits. These nodes exist, but you usually don’t see them. Their swelling is the result of the lymphatic system activating near the area where the immune response starts (such as when you have tonsillitis: the lymph nodes grow in the throat).
What to do ?
Be sure to move your arm after the injection, and then continue using your arm normally even if it hurts. Do not leave your arm static, as it is necessary to stimulate blood circulation. If this gets you started, you can also put a small cold compress, like after pain from intense sports exercise or a bruise.
It is indeed what the CDC advises : « Apply a clean, cool and damp washcloth to the affected area » and « use your arm or exercise ». Obviously, this is about exercising in a moderate way, the equivalent of small warm-ups.
On the app TikTok, an astonishing non-medical practice has gone viral in the United States: people advise turning the arm, 15 to 30 minutes after the injection, as if you were making some kind of windmill. According to these Internet users, this would help calm the pain. Yes it promotes blood circulationHowever, this is not a scientifically proven recommendation against the pain created by the vaccine. It can’t hurt as long as you don’t overdo it (and avoid hitting a wall or something in the process, it will only increase the pain), and then keep moving your body. arm normally, which remains the most recommended medically.
How to spot an allergy?
If your arm hurts, and / or you have redness or swelling of the glands, this is not a sign of an allergy or a problem, but, as we explained above, it this is a normal reaction. On the other hand, if these effects persist for more than 3 days or worsen by becoming really bothersome, this may be a sign of an allergy, so you should tell your doctor.
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Source: Numerama by www.numerama.com.
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