Eight delivery platforms. Every licensed human vaccine maps to one.
Each platform encodes a fundamentally different answer to the question: how do you present a foreign antigen to the immune system safely and durably? The choice of platform determines thermostability, manufacturing complexity, innate immune activation profile, and suitability for rapid redesign.
mRNA
LNP-encapsulated synthetic mRNA. Host ribosomes translate the antigen — no viral genome, no integration. Fastest platform to redesign (days).
Recombinant Subunit
Purified recombinant antigen + adjuvant (Matrix-M, AS01B). No nucleic acid. Longest safety track record; excellent for protein antigens.
Inactivated Whole-Virion
Formalin or BPL-killed whole pathogen presenting native antigens. Refrigerator-stable; established in low-income settings.
Live-Attenuated
Replication-competent organism with reduced pathogenicity. Strongest cellular and trained innate immunity; typically single dose.
Toxoid
Formalin-inactivated bacterial exotoxin. Immunity targets the toxin; durable humoral response; simple manufacturing.
VLP
Recombinant virus-like particles (L1, HBsAg) — no nucleic acid. Dense multivalent antigen display drives strong B-cell responses.
Conjugate
Polysaccharide capsular antigens conjugated to carrier protein (CRM197). Converts TI-2 to T-cell-dependent response; enables infant immunisation from 6 weeks.
mRNA Vaccines
LNP-encapsulated synthetic mRNA encoding the target antigen is delivered to host cells, where ribosomes translate it into protein — triggering both innate and adaptive immunity. No viral genome component; no integration risk. The antigen sequence can be redesigned in days once a pathogen genome is sequenced, making this the fastest platform known. Pseudouridine substitution reduces innate immune sensing of the mRNA while preserving translational efficiency. Lipid nanoparticles (LNP) are critical: ionizable lipid, PEG-lipid, phospholipid, and cholesterol work together to protect mRNA from degradation and enable endosomal escape.
Viral Vector Vaccines
Replication-incompetent adenoviruses (ChAdOx1 from chimpanzee; Ad26 from human) are engineered to carry the antigen gene into host cells. The adenovirus capsid provides potent innate immune stimulation via TLR and cytosolic sensing pathways — an adjuvant effect built into the vector itself. Single-dose regimens are feasible. A rare but serious adverse event specific to adenovirus-vectored COVID-19 vaccines is VITT (vaccine-induced immune thrombocytopenia and thrombosis), mediated by anti-PF4 antibodies that activate platelets, occurring at ~1:100,000 doses.
Recombinant Subunit Vaccines
A purified recombinant antigen protein is co-administered with an adjuvant — Matrix-M (saponin-based, Novavax), AS01B (MPL + QS-21, GSK), or alum. No nucleic acid component; no viral element. The antigen can be produced in yeast, insect cells (baculovirus system), or mammalian cells. Adjuvants are critical: without them, protein alone elicits weak cellular immunity. This platform has the longest clinical safety track record of any modern vaccine technology. It is the approach used for hepatitis B, HPV (original Cervarix/Gardasil), and influenza subunit vaccines.
Inactivated Whole-Virion Vaccines
The whole pathogen is grown, then chemically inactivated — with formalin (formaldehyde cross-links nucleic acid and proteins) or β-propiolactone (BPL, alkylates nucleic acids while preserving surface protein epitopes). The result presents a broad array of native surface antigens to the immune system. Alum adjuvant is typically included. These vaccines are thermostable under refrigeration, do not require ultra-cold storage, and their manufacturing technology is well-established in low- and middle-income countries. The trade-off is that they may require higher antigen loads and more doses than nucleic acid platforms.
Live-Attenuated Vaccines
A replication-competent organism with dramatically reduced pathogenicity — achieved by serial passage (BCG, measles, rotavirus), codon de-optimization, or targeted gene deletion. Because the organism replicates in the host, it presents antigens in a native context over time, generating the strongest CD8&sup+ T-cell responses, durable B-cell memory, and trained innate immunity (epigenetic reprogramming of myeloid cells). Typically a single dose provides lifelong protection. Key risks: potential reversion to virulence (mitigated by multiple attenuating mutations) and contraindication in severely immunocompromised individuals. Cold-chain requirements are often more demanding than inactivated vaccines.
Toxoid Vaccines
Formalin-inactivated bacterial exotoxins retain immunogenicity while losing toxicity. Because the clinical disease is caused by the exotoxin (tetanospasmin, diphtheria toxin) rather than the bacterium itself, immunity directed at the toxin is sufficient for complete protection. Aluminium salt adjuvants (alum) are used to potentiate the response. Protection is humoral: neutralising IgG antibodies block toxin binding to host cell receptors. Immunity wanes over 5–10 years, necessitating boosters. Toxoid vaccines are among the simplest to manufacture and thermally stable under refrigeration. Used in combination vaccines: DTP, DTaP, Tdap, DT, Td.
VLP Vaccines
Recombinant virus-like particles are self-assembling structures built from viral structural proteins (HPV L1 pentamers, hepatitis B surface antigen — HBsAg) but containing no nucleic acid genome. They cannot replicate. The dense, repetitive surface antigen display — mimicking the geometry of a native virus particle — is extraordinarily efficient at cross-linking B-cell receptors, driving germinal centre reactions and high-titre, durable neutralising antibody responses without adjuvant in some formulations (though AS04 is used in Cervarix). Manufacturing is more complex than simple protein subunits because the VLP must self-assemble correctly, but it is far simpler than growing live virus. HPV VLP vaccines are among the most efficacious vaccines ever developed.
Conjugate Vaccines
Polysaccharide capsular antigens from encapsulated bacteria (Streptococcus pneumoniae, Haemophilus influenzae type b, Neisseria meningitidis) are individually conjugated to a carrier protein — most commonly CRM197 (a non-toxic diphtheria toxin mutant) or tetanus toxoid. This conjugation converts a T-cell-independent (TI-2) polysaccharide antigen into a T-cell-dependent one, enabling germinal center reactions, affinity maturation, memory B-cell formation, and effective immunisation of infants as young as 6 weeks. The central immunological innovation of the conjugate platform — first established for Hib vaccine by Robbins and Schneerson — is responsible for the near-elimination of invasive H. influenzae type b disease and the dramatic reduction in pneumococcal and meningococcal invasive disease across all age groups.
Help expand the Vaccine Atlas
Every entry follows the same schema: structured frontmatter, peer-reviewed trial citations, mechanistic detail on antigen format and immune readout, and cross-atlas links to the pathogen and host biology atlases. The goal is to map every licensed vaccine at the same depth — platform, adjuvant, cold-chain, trial efficacy, and adverse event profile.