Which statement best describes a live attenuated vaccine?

Which statement best describes a live attenuated vaccine?

• A. Vaccines containing a live but weakened form of the pathogen.
• B. Vaccines made from killed pathogens.
• C. Vaccines that use only specific protein components.
• D. Vaccines that inactivate toxins.

Answer: (A)

Live attenuated vaccines contain a live but weakened form of the pathogen. Because it is still alive, it can replicate briefly in the body, which presents the immune system with a broad range of antigens in a way that closely mimics natural infection. This strong exposure triggers both antibody responses and T-cell responses, often giving long-lasting immunity with fewer doses. Examples include vaccines for measles, mumps, rubella, and varicella. This differs from vaccines made from killed pathogens (which cannot replicate and may require boosters), subunit vaccines that use only specific protein pieces, and toxoid vaccines that inactivate toxins. A consideration is that, since the agent is alive, it can pose risks to people with weakened immune systems and, rarely, can revert to a more virulent form, so such vaccines are used with precautions in certain groups.

Live attenuated vaccines contain a live but weakened form of the pathogen. Because it is still alive, it can replicate briefly in the body, which presents the immune system with a broad range of antigens in a way that closely mimics natural infection. This strong exposure triggers both antibody responses and T-cell responses, often giving long-lasting immunity with fewer doses. Examples include vaccines for measles, mumps, rubella, and varicella. This differs from vaccines made from killed pathogens (which cannot replicate and may require boosters), subunit vaccines that use only specific protein pieces, and toxoid vaccines that inactivate toxins. A consideration is that, since the agent is alive, it can pose risks to people with weakened immune systems and, rarely, can revert to a more virulent form, so such vaccines are used with precautions in certain groups.