Final answer:
Adverse reactions to vaccines typically occur after the vaccination and most are not life-threatening. Severe allergic reactions like anaphylaxis are rare, and not all adverse reactions are related to vaccine allergies.
Step-by-step explanation:
The statement about vaccine adverse reactions that is TRUE is that adverse reactions may occur after vaccination. Adverse reactions to vaccines can range from mild to severe, but it is important to note that most vaccine adverse reactions are not life-threatening. Rather, they can be minor side effects such as soreness at the injection site or a mild fever. Severe allergic reactions like anaphylaxis are rare, but they can happen. This is why observation after vaccination is recommended. Importantly, adverse reactions do not occur before vaccination, as they are a response to the vaccine itself. Furthermore, while allergies can cause adverse reactions to vaccines, not all adverse reactions are related to allergies. Most adverse reactions are milder and unrelated to allergic responses.