Explanation:

- Option 1: Live-attenuated vaccines use a weakened form of the pathogen. They are not used for diphtheria.

- Option 2: Viral Vector vaccines utilize modified viruses to deliver the pathogen's genes. They are not used for diphtheria.

- Option 3: Toxoid vaccines protect against diseases, like diphtheria, caused by bacterial toxins. They contain inactivated toxins that trigger an immune response without causing disease.

- Option 4: mRNA vaccines introduce genetic material to instruct cells to produce a protein that triggers immunity. They are not used for diphtheria.

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