Fig. 1

Panoramic landscape of the strategies used for vaccine development and delivery. a The live attenuated vaccine strategy consists of administering a weakened form of a live pathogen. This strategy usually elicits robust and long-term memory immune responses after a single dose. b The inactivated pathogen vaccine strategy also consists of administering a whole pathogen, but in this case, inactivated by heat or chemical treatment. This strategy has a better safety profile but often is found to be less immunogenic. c In contrast with whole pathogen strategies, subunit vaccine strategies include administering only the most immunogenic antigens of a pathogen. These strategies commonly require adjuvant addition to triggering robust immune responses. Protein subunit vaccines are the most prominent members of this group. d Another type of subunit vaccine is polysaccharide vaccines. This strategy consists of administering long chains of sugar molecules that make up certain bacteria’s surface capsules. However, polysaccharides are T-independent antigens, eliciting low quality and short-term immune responses, especially in children. e To tackle this disadvantage, conjugated vaccines were perceived. This strategy uses a molecule composed of a polysaccharide antigen fused or conjugated to a carrier-protein antigen that induces long-term immunological memory, isotype switching, and affinity maturation processes. f The virus-like particle strategy is the last member of the subunit vaccine group. In this case, antigens are expressed in recombinant yeast cells, vaccinia virus or tobacco mosaic virus transfected organisms, and subsequently self-assembled in virus-like particles whose size and conformation induce their capture from host antigen-presenting cells, eliciting solid immune responses post-administration. g The viral vector vaccine strategy consists of applying a genetically manipulated measles or adenoviral platform to express a foreign antigen to trigger robust immune responses. h Finally, the nucleic acid vaccine strategies (DNA and mRNA) codify the pathogen’s immunogenic proteins. Once administered, the genetic material is captured by myocytes or antigen-presenting cells that use it to express and present the antigen to the host immune system