A high fever after receiving the 23-valent pneumonia vaccine is usually caused by an allergic reaction, or it may be caused by other illnesses. 1. Allergic reaction: 23-valent pneumonia vaccine is an inactivated vaccine with no live bacterial components, which usually does not lead to infection and cause high fever. However, since the vaccine contains certain antigenic components of Streptococcus pneumoniae, these components may lead to excessive immune response of the body, causing an allergic reaction and leading to high fever, rash and other related symptoms. 2. Caused by other diseases: High fever caused by allergic reaction after receiving 23-valent pneumonia vaccine is usually transient and will be relieved relatively quickly. If the patient has a persistent high fever, it may be caused by influenza or tuberculosis, and requires prompt medical attention. If you have a high fever after receiving the 23-valent pneumonia vaccine, you need to consult your doctor and take care of it under their supervision.