A large area of redness and swelling occurred after receiving the quadrivalent vaccine.

Generally, the quadrivalent vaccine is a combination vaccine made by combining four different antigens: pertussis vaccine, tetanus vaccine, diphtheria vaccine, and Haemophilus influenzae type b (Hib) vaccine. Redness and swelling over a large area after administration of the quadrivalent vaccine may be caused by needle puncture injury, local infection, or allergic reaction. Patients can receive symptomatic treatment based on the specific cause. The details are as follows:

1. Needle puncture injury: During administration of the quadrivalent vaccine, the needle penetrates the skin, causing tissue trauma and an inflammatory response, leading to local vasodilation, congestion, and consequently redness and swelling of the skin. This is a normal phenomenon that does not require special treatment. Such swelling usually resolves spontaneously within three days.

2. Local infection: If the needle used for administering the quadrivalent vaccine is contaminated, it may lead to infection at the injection site, resulting in symptoms such as redness, pain, and pus formation. Under medical guidance, patients may use medications such as mupirocin ointment or erythromycin ointment for treatment, while maintaining good hygiene at the injection site.

3. Allergic reaction: Individuals with special constitutions who are allergic to one of the components in the quadrivalent vaccine may develop allergic symptoms after vaccination, including skin redness, swelling, and pain. Under medical supervision, patients may use calamine lotion or hydrocortisone butyrate cream for treatment, and should avoid scratching the injection site.

If redness and swelling occur after receiving the quadrivalent vaccine, it is recommended to seek timely medical attention to prevent delayed diagnosis and treatment.