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What is a Messenger (mRNA) Vaccine? The New COVID-19 Vaccines Explained

Posted by Michelle Walters on 4th Mar 2021

The new Moderna and Pfizer vaccines developed for COVID-19 are an entirely new type of vaccine that does not include the virus. They care called mRNA vaccines, or messenger vaccines. How do they differ from traditional vaccines, and what makes them such an exciting scientific breakthrough?

Key Points1

  • mRNA vaccine technology is new, but the concept has been studied for decades.
  • mRNA vaccines do not contain a live virus and do not carry a risk of causing disease.
  • mRNA from the vaccine never enters the nucleus of the cell and does not interact with a person’s DNA.

How traditional vaccines work2

Viruses contain a core of genes made of DNA or RNA wrapped in a coat of proteins. To make the protein coat, the virus creates messenger RNA (mRNA) which then makes the proteins.

The main goal of a vaccine for a particular disease is to teach a person's immune system how to recognize and attack a virus if it ever enters the body. Historically this has been done by teaching the body to recognize the DNA or RNA of the virus itself.

Most traditional vaccines use weakened or inactivated versions (or components) of the disease-causing pathogen to stimulate the body’s immune response to create antibodies. These traditional vaccines work very well and have gone a long way toward eradicating or minimizing diseases like polio and measles. One downside, however, is that growing large amounts of a virus, and then weakening or dividing the virus for use in the vaccine, takes a long time.

This new type of mRNA vaccine teaches the body to recognize a disease by its messenger proteins, it's mRNA, instead of the virus itself.

Because any protein can be encoded and expressed by mRNA, in theory mRNA vaccines could be developed to fight diseases for many viruses and possibly even cancer. This is what makes this nacent technology such a thrilling concept. 3 mRNA vaccines can be developed in a laboratory using a DNA template and readily available materials, meaning the entire process can be standardized and quickly scaled up. There is no need to slowly grow viruses and process them.

Benefits of mRNA Vaccines

This new form of mRNA vaccine has several benefits:

  • uses non-infectious elements and does not interact with the genome
  • outstanding safety profile
  • shorter manufacturing times / easier scaling
  • potential for targeting of multiple diseases at once

Early steps toward mRNA vaccines2

About 30 years ago, a handful of scientists began exploring whether vaccines could be made more simply. What if you knew the exact structure of the mRNA that made the critical piece of a virus’s protein coat, such as the spike protein of the COVID-19 virus?

It is relatively easy to make that mRNA in the laboratory, in large amounts. What if you injected that mRNA into someone, and the mRNA then traveled through the bloodstream to be gobbled up by immune system cells, and then those cells started to make the spike protein? Would that teach the immune system to recognize and fight off future attacks from the virus?

Overcoming obstacles in creating mRNA vaccines

While the concept seems simple, it required decades of work to overcome various hurdles. First, scientists learned how to modify mRNA so that it did not produce violent immune system reactions. Second, they learned how to encourage immune system cells to gobble up the mRNA as it passed by in the blood. Third, they learned how to coax those cells to make large amounts of the critical piece of protein. Finally, they learned how to enclose the mRNA inside microscopically small capsules to protect it from being destroyed by chemicals in our blood.

Along the way, they also learned that, compared to traditional vaccines, mRNA vaccines can actually generate a stronger type of immunity: they stimulate the immune system to make antibodies and immune system killer cells — a double strike at the virus.

Then came the pandemic

So, 30 years of research allowed several groups of scientists — including a group at Pfizer working with a German company called BioNTech, and a young company in Massachusetts called Moderna — to bring mRNA vaccine technology to the threshold of actually working. The companies had built platforms that, theoretically, could be used to create a vaccine for any infectious disease simply by inserting the right mRNA sequence for that disease.

Then along came COVID-19. Within weeks of identifying the responsible virus, scientists in China had determined the structure of all of its genes, including the genes that make the spike protein, and published this information on the Internet.

Within minutes, scientists 10,000 miles away began working on the design of an mRNA vaccine. Within weeks, they had made enough vaccine to test it in animals, and then in people. Just 11 months after the discovery of the SARS-CoV-2 virus, regulators in the United Kingdom and the US confirmed that an mRNA vaccine for COVID-19 is effective and safely tolerated, paving the path to widespread immunization. Previously, no new vaccine had been developed in less than four years.

No scientific breakthrough stands alone

Already, mRNA vaccines are being tested for other infectious agents, such as Ebola, Zika virus, and influenza. Cancer cells make proteins that also can be targeted by mRNA vaccines: indeed, recent progress was reported with melanoma. And theoretically, mRNA technology could produce proteins missing in certain diseases, like cystic fibrosis.

Like every breakthrough, the science behind the mRNA vaccine builds on many previous breakthroughs, including

  • understanding the structure of DNA and mRNA, and how they work to produce a protein
  • inventing technology to determine the genetic sequence of a virus
  • inventing technology to build an mRNA that would make a particular protein
  • overcoming all of the obstacles that could keep mRNA injected into the muscle of a person’s arm from finding its way to immune system cells deep within the body, and coaxing those cells to make the critical protein
  • and information technology to transmit knowledge around the world at light-speed.

Every one of these past discoveries depended on the willingness of scientists to persist in pursuing their longshot dreams — often despite enormous skepticism and even ridicule — and the willingness of society to invest in their research.