What’s the Cause of the Small Red Spot on the Little Girl’s Right Arm?

A 3-year-old girl developed a small red spot on her right arm (where she received her vaccine) about 3 to 4 months after birth. Initially, it was thought to be a reaction to the vaccination, but several small red dots appeared later, which have now merged into a red bump the size of a small fingernail, resembling a strawberry. What is this condition? How should it be treated? Is surgery needed? Is it dangerous?
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