For a vaccine to be effective, the components of the disease of interest that provide protection from disease (an antigen) must be incorporated or present in the candidate and induce a strong and appropriate immune response in the vaccine. Viral vaccines specifically can be classified into ‘classic or traditional vaccines’ and include attenuated/killed virus. Recombinant vaccines include subunit, virus-like particle (VLP), conjugate, and viral-vectored vaccines. Genetic vaccines include messenger RNA (mRNA)/DNA. Alternatively, vaccines can be classified into live and non-live vaccines, which is important when considering safety profiles.