Vaccinantigen

Vaccinantigen refers to the molecule within a vaccine that is recognized by the immune system and triggers an adaptive immune response. It is the immunogenic component designed to induce protection against a specific pathogen or toxin. Vaccinants can be whole organisms that have been attenuated or inactivated, or defined components such as proteins, peptides, polysaccharides, toxoids, or nucleic acids that encode an antigen.

Vaccines deploy vaccinants in several formats. Subunit vaccines use a single antigen or a few antigens. Conjugate vaccines link polysaccharide antigens to carrier proteins to improve immunogenicity, especially in young children. Vaccines based on nucleic acids (DNA or RNA) or viral vectors deliver genetic information that instructs host cells to produce the antigen. In some cases the whole organism is used but inactivated or attenuated to reduce virulence while retaining antigenic properties.

The goal of selecting a vaccinantigen is to present epitopes that elicit protective neutralizing antibodies and/or robust T-cell responses. Effective presentation to B and T cells often depends on adjuvants or delivery systems that enhance magnitude and durability of the response. Vaccinants are evaluated for safety, stability, and potential cross-protection; pathogen variability can necessitate updates or multicomponent formulations. Examples of vaccinantigens include influenza hemagglutinin, measles and rubella virus antigens, diphtheria and tetanus toxoids, pneumococcal polysaccharide conjugates, and the SARS-CoV-2 spike protein used in many vaccines.