A traditional vaccine carries the microbe it wants to introduce to the immune system — killed, weakened or broken up — in a biological process that takes months to manufacture. mRNA vaccines skip that step: the cell is handed a piece of messenger RNA telling it to make the protein from the virus's surface itself. The body produces the protein, the immune system learns it, and the mRNA degrades within days.

The idea was not new; it had been worked on since the 1990s and had two basic problems — bare mRNA broke down before entering the cell, and once inside triggered a violent immune reaction. The solution published by Katalin Karikó and Drew Weissman in 2005, based on modifying one of RNA's building blocks, suppressed that reaction, while lipid nanoparticle carriers delivered the molecule into the cell. Without those two advances the speed of 2020 would have been impossible; Karikó and Weissman received the Nobel Prize in Medicine in 2023.

When the sequence of SARS-CoV-2 was published in January 2020, designing the vaccine took days; the remaining eleven months went to clinical trials, manufacturing and regulatory review. This compressed a process whose previous record was four years, largely through trials run in parallel and manufacturing risk taken in advance. The result was not distributed evenly: through 2021 vaccination rates passed seventy per cent in high-income countries while remaining around ten per cent in low-income ones, and the argument over a patent waiver continued at the World Trade Organization. The same platform is now being tested for influenza, RSV and individually tailored cancer vaccines.