What is a major adverse effect of vaccines?

• A. headache
• B. fever
• C. rash
• D. anaphylaxis (severe allergic reaction)

Answer: (D)

A major concern with vaccines is the rare possibility of anaphylaxis, a severe, life-threatening allergic reaction that can occur after vaccination. It happens when the immune system overreacts to a vaccine component and typically appears within minutes to a few hours. Signs include swelling of the throat or lips, trouble breathing, hives, dizziness, and a drop in blood pressure. Because of this risk, vaccination sites monitor recipients for a short period after administration and are prepared to treat anaphylaxis immediately with epinephrine and emergency care. In contrast, headache, fever, and rash are common, usually mild, and self-limiting, so they don’t carry the same level of immediate danger. Recognizing this rare but serious adverse event helps underscore why vaccines are administered in settings equipped to manage it quickly, while the overall benefit of vaccination remains very high.