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Hi and welcome.
There can be two reasons for your problem following an injection into your musce, one might be that you had some injury and inflammation within the muscle due to vaccine itself and second is you might have injury to your nerve which pass nearby that muscle. I would suggest you to visit your doctor and get it examined for exact diagnosis and to rule out any infection or abcess in there. Moreover, regular massage of the area with olive oil and physiotherapy of the injected arm can improve your pain and movement.
Let me know if you have further questions.
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Wish you good health.