COVID-19 (Coronavirus)
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mRNA Vaccines: An Explanation

An illustration of mRNA vaccine.

Illustration: Dan Page

How Does the Vaccine Work?

Imagine a coded message being smuggled into your cells, offering instructions on how to make a special protein. Your cell reads the message and orders its tiny factories to manufacture the new protein, then rips up the instructions.

Now the protein bubbles to the surface of the cell, touching off a series of immune system reactions. White blood cells known as B cells and T cells spring into action. The T cells recognize an intruder and help B cells start making antibodies. Certain T and B cells will “remember” this foreign protein, ready to mobilize if this culprit infiltrates the body again.

Moshe Arditi, MD, academic director of the Division of Infectious Diseases at Cedars-Sinai

Moshe Arditi, MD

That’s essentially how the vaccines using messenger RNA (mRNA) to protect against COVID-19 infection work, explains Moshe Arditi, MD, academic director of the Division of Infectious Diseases at Cedars-Sinai and the GUESS?/Fashion Industries Guild Chair in Community Child Health.

“More than 17 years of research brought us to this point. This one protein—called the spike protein—is both what the virus uses to infect us and is also the virus’ Achilles heel,” Arditi says. “The mRNA vaccines turn our own bodies into a factory, teaching our cells how to make that viral protein so that we can raise an immune response against it.”

Traditional vaccines use a weakened or dead virus—or a tiny portion of live virus—to spark the immune system. The mRNA model more closely mimics what happens in the body with an actual infection, but with only a single, crucial protein rather than the virus itself, potentially resulting in a more powerful immune response.

Messenger RNA is sometimes referred to as the “software of life,” Arditi says. These molecules give instructions from our DNA to our cells to carry out all the processes necessary for life. Scientists have studied mRNA as a potential tool to treat diseases, such as cystic fibrosis, that are caused by the body failing to make certain proteins—and it’s also been studied as a delivery system for cancer therapies.

“These vaccines are also less challenging to make than traditional vaccines,” Arditi says. “We’ve had three pandemics in the last 20 years caused by coronaviruses, including SARS and MERS. It’s incredible that scientists were able to develop specific COVID-19 vaccines so quickly. We’ve learned a lot about the approach, so the next time this happens, we could have a vaccine already made and ready to ship before the pandemic takes over.”