Most of the vaccinations usually cause redness and swelling in the deltoid region of the shoulder, mostly due to an immune reaction of the body after the vaccination. Some patients may have a slightly heavier reaction, with a non-specific redness after the injection, but it is not particularly serious and can gradually subside or even disappear in 2-3 days. The injection site must be kept dry and avoid contact with water, especially when redness, swelling, itching and pain do not scratch with your hands to prevent secondary infection. You should eat a light diet and avoid spicy and irritating foods. In addition, if the redness and swelling is particularly serious, you can properly apply Bactrim around the anti-inflammatory and pain relief. However, if the redness and swelling are particularly severe, or even if there is pus or generalized fever, you must go to the hospital for detailed diagnosis and treatment to exclude the possibility of serious allergic reaction or septic infection of the vaccine.