There are various possibilities of local redness and swelling after vaccination, the common ones are local injection reaction and delayed local reaction, which can be temporarily observed and relieved by cold compresses. Local injection reaction: It is the most common situation and usually starts to appear within 24 hours after injection. No treatment is needed and it can subside after 2~3 days. If swelling and pain are obvious, ice packs can be used to relieve symptoms. If skin rash, angioedema and other systemic symptoms appear, you should go to the hospital in time. Delayed local reaction: It is a delayed allergic reaction, which usually occurs a few days after vaccination and lasts for about 3~4 days, and can gradually subside on its own without treatment. It is recommended to go to the hospital for treatment according to medical advice.