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How mRNA herpes vaccines work

Last updated: July 1, 2026

Several of the most-watched herpes vaccine candidates use mRNA — the same technology behind the COVID-19 vaccines. This explainer covers how an mRNA vaccine delivers instructions for a cell to make selected viral proteins, why several HSV programs chose the approach, and why a platform that works for one disease is not proof it will work for another.

The short answer

Several of the most-watched herpes vaccine candidates now in or near clinical testing are mRNA vaccines — built on the same class of technology used in the COVID-19 vaccines. Rather than injecting a piece of the virus itself, an mRNA vaccine delivers genetic instructions that tell a person’s own cells to make selected viral proteins, so the immune system can learn to recognize them. [S1][S2]

How an mRNA vaccine works, step by step

An mRNA vaccine starts from an everyday molecule your cells already use. mRNA — short for messenger RNA — is the working copy of a gene: it carries protein-making instructions from the DNA in a cell’s nucleus out to the cell’s protein-making machinery. An mRNA vaccine simply supplies a lab-made version of that molecule, one written to code for a chosen viral protein or set of proteins. [S1]

On its own, mRNA is fragile and would be broken down almost immediately if injected bare. To prevent that, the mRNA is wrapped in a lipid nanoparticle (LNP) — a microscopic fatty sphere that shields the mRNA and helps ferry it into cells. Lipid nanoparticles are the delivery system that carried mRNA into routine clinical use; they protect the genetic material from degradation and enable cells to take it up and release it inside. [S4]

Once the mRNA is inside a cell, the cell reads the instructions and manufactures the viral protein or proteins. These proteins act as antigens — the molecular flags that the immune system reacts to. In response, the immune system mounts a defense built around two main players: antibodies, Y-shaped proteins that latch onto a specific target and can block or tag it, and T cells, immune cells that recognize infected cells and coordinate or carry out their destruction. Both are now trained to recognize the real virus if it ever appears. The vaccine mRNA itself is short-lived: it works in the cell’s cytoplasm, is broken down by the cell after doing its job, and does not enter the nucleus or alter a person’s DNA. [S1][S4]

Why so many HSV programs chose mRNA

One reason is flexibility. The mRNA approach makes it straightforward to encode several viral proteins in a single vaccine. That suits herpes simplex virus (HSV) well, because researchers want to target not only the protein the virus uses to enter cells but also the proteins it uses to hide from the immune system. This is the reasoning behind the trivalent gC2/gD2/gE2 design: gD2 is an entry antigen, while gC2 and gE2 are immune-evasion proteins — gC2 interferes with the complement system, and gE2 binds the tail (Fc) end of antibodies to blunt their effect. Adding antigens that counter these evasion tricks, alongside the entry antigen, is the strategy behind this multi-protein design. [S3][S1]

The leading HSV mRNA candidates tracked here reflect that thinking. BNT163 (BioNTech) is a prophylactic candidate — that is, one aimed at preventing infection — and is a trivalent mRNA vaccine encoding gC2/gD2/gE2 wrapped in lipid nanoparticles. mRNA-1608 (Moderna) is a therapeutic candidate — one aimed at reducing disease in people already infected rather than preventing infection. Both trace back to the trivalent approach developed at the University of Pennsylvania (the Awasthi and Friedman work), which BNT163 is based on. [S1][S2]

What this does and does not mean

mRNA is a delivery platform, not a guarantee of success. Its performance against COVID-19 does not establish that it will work against HSV, which is a harder target: the virus establishes latency — a dormant state in nerve cells from which it can reactivate — and it actively evades the immune system. Distinctions matter here. A vaccine designed to prevent infection (prophylactic) is not the same as one designed to treat an existing infection (therapeutic); results in animals are not results in people; and a trial existing is not the same as a trial succeeding. As of this update, the HSV mRNA candidates remain early-stage or unproven in humans. BNT163 is in a Phase 1 trial — the first and smallest stage of human testing, focused on safety. [S2][S1] Moderna’s mRNA-1608 program has since ended: its Phase 1/2 trial reached completion in 2025 [S5], and Moderna announced that the program will not advance to Phase 3 [S6]. A platform that works for one disease is not proof that it works for another. [S2][S1]