mRNA vaccines helped us through the COVID-19 pandemic, with a technology that became the basis for several coronavirus vaccines. What is behind the success of this technology? And what other applications can it have in the future? Can it help us defend against other infectious diseases and offer general protection against the flu, and even treat cancer?

What are mRNA vaccines and how do they work?

All vaccines introduce a harmless particle of a particular bacterium or virus into the body, causing an immune response. Most vaccines contain weakened or killed bacteria or viruses. However, scientists have developed a new type of vaccine that uses a molecule called messenger RNA (or mRNA), instead of part of a bacterium or virus. Messenger RNA is a type of RNA necessary for the production of proteins. In cells, mRNA uses information from genes to create a blueprint for making proteins. Once cells finish making a protein, they quickly break down the mRNA. The mRNA from the vaccines does not enter the nucleus and does not alter the DNA.

mRNA vaccines work by introducing a fragment of mRNA that corresponds to the viral protein, usually a small fragment of a protein found on the outer membrane of the virus. (People who receive an mRNA vaccine are not exposed to the virus and cannot be infected by the vaccine.)

These vaccines are not based on injecting part of a virus into a person, like many others; instead they carried a genetic code that our bodies could use to make the key piece of the viral protein. The entire process is faster and easier, and, among other things, it avoids the need to grow the virus in a laboratory and purify the proteins resulting from the process. Using this mRNA template, the cells produce the viral protein. As part of a normal immune response, the immune system recognizes that the protein is foreign and produces specialized proteins called antibodies.

While the first approved mRNA vaccines were for COVID-19, similar vaccines are already being explored for a lot of diseases. Malaria, HIV, tuberculosis and Zika are just some of the possible targets. The mRNA vaccines could also be used in personalized cancer treatments. The idea is to provoke a specific response from the immune system, designed to attack tumor cells in the body.

Vaccines are cheap, quick and easy to make, says Katalin Karikó, associate professor at the University of Pennsylvania, a pioneer in research on the use of mRNA for vaccines. They are also very efficient. "When you introduce [the mRNA] into the cells, half an hour later, they are already making the protein," she explains.

The idea is that once the immune system has been exposed to such a protein, it will be better positioned to mount a strong response if it ever encounter the virus itself.

In theory, we could make mRNA for virtually any protein and perhaps attack any infectious disease. It is an exciting time for mRNA vaccine technology, and several vaccines for many infectious diseases are currently in the clinical trial phase.

In the same way that we can train our immune system to recognize viral proteins, we can also train it to recognize proteins in cancer cells. In theory, this approach could be fully personalized: Scientists could study a specific person's tumor cells and create a personalized treatment that would help that person's own immune system defeat the cancer.