Toxoid vaccines are defined by using inactivated toxins; which of the following statements is true?

• A. Uses inactivated toxins that preserve immunogenicity; Example: tetanus toxoid.
• B. Uses live toxins to provoke response.
• C. Uses whole bacteria to induce immunity.
• D. Uses viral vectors to deliver antigens.

Answer: (A)

Toxoid vaccines work by using inactivated toxins that still resemble the toxin enough for the immune system to recognize them and generate neutralizing antibodies. The toxin is chemically or heat-inactivated so it can’t cause disease, but its protein structure preserves epitopes that B cells use to make antibodies. Those antibodies can then neutralize the real toxin if exposure occurs, preventing illness. Tetanus toxoid is a classic example of this approach.

The other options don’t describe toxoid vaccines. Using live toxins would be dangerous and is not how vaccines are given. Using whole bacteria triggers immunity to many bacterial components, not specifically the toxin. Viral vectors deliver different antigens via a virus, not the inactivated toxin form used in toxoids.