A Level Biology Practice Exam

What characteristic defines a safe form of an antigen used in vaccines?

1. It is non-infectious

2. It can cause an immediate immune response

3. It is harmful to the host

4. It can replicate in the body

The correct answer is: It is non-infectious

The correct answer highlights that a safe form of an antigen used in vaccines is non-infectious. This characteristic is crucial because vaccines are designed to stimulate the immune system without causing the disease they aim to protect against. An antigen that is non-infectious means it cannot cause illness, allowing the body to recognize and respond to it safely, which helps build immunity without risk to the individual. In contrast, an antigen that can cause an immediate immune response may not be safe if it is infectious or harmful to the host. Similarly, antigens that are harmful or capable of replicating in the body pose significant health risks and would be unsuitable for prevention of disease through vaccination. Thus, the safety and effectiveness of vaccines rely heavily on the use of non-infectious forms of antigens.