How mRNA Vaccines Work

mRNA vaccines have to potential to end the COVID19 pandemic. How do they work? Are they safe? And how could they’ve been developed so quickly?

The main idea of mRNA vaccines is to trick our bodies to produce part of a virus. This kickstarts our immune response, without getting us sick. All that’s needed is a part of the virus’s DNA or RNA, packaged into mRNA. Cool!

Follow-up: Questions & Answers

Making a video about vaccines means getting a lot of questions and remarks. Below are some of the most frequently asked questions about mRNA vaccines, specifically the ones for SARS-CoV-2. I tried to answer each one to the best of my ability.

Once again: I’m not asking you to trust me. Please don’t. I am no doctor, biologist, or immunologist. That’s why I’ve listed my sources below each answer. Up to you to determine if these seem trustworthy to you.

If you have additional questions or suggestions for improvements: write a comment below, contact me on Twitter or reply to my video.

Is this video sponsored by the pharmaceutical industry?

No, this video was not sponsored by anyone. It was made on my own initiative, with my own research. So far, none of the Simply Explained videos have been sponsored.

Taking money from a pharmaceutical company to make this video would instantly destroy my credibility.

Source: myself.

Does the vaccine prevent the virus from spreading? Why can vaccinated people still test positive for SARS-CoV-2?

This viewer correctly points out that the vaccine will not prevent the virus from spreading. The vaccine will train your body’s immune system, but that immunity is built up in your bloodstream.

The coronavirus enters your body mostly via the nose, where it is replicated in the mucus membranes. Our vaccines, however, are injected into other parts of the body and trigger an immune response in your bloodstream. In other words: your body will produce antibodies.

At this stage, however, it’s unclear if those antibodies will find their way to the nasal mucosa. If few antibodies are present there, the virus could replicate in your nose and infect others when you sneeze. The 90-95% effectiveness of vaccines points to the fact that you’re unlikely to get sick from an infection.

In summary: the vaccine will protect you from future infections but might not prevent you from spreading the virus to others. This is currently being researched in clinical trials.


Why can’t we use traditional vaccines?

We do have traditional vaccines for COVID19. The Chinese vaccine (CoronaVac, developed by Sinovac) uses inactivated SARS-CoV-2 virus particles to train our immune system. Because they are “inactivated,” they can no longer make you sick.

Other types of vaccines are also being developed. GSK/Sanofi, for instance, uses a special process to extract the spikes from real, lab-grown coronaviruses. In theory, this should trigger the same immune response as the mRNA vaccines, but without instructing our cells to produce the spikes themselves.


Can the vaccine alter our DNA? Become a part of us?

mRNA vaccines can enter our cells and make them produce the Spike protein, but it cannot enter the cell nucleus, where our DNA is stored.

Fun fact: a virus “that becomes a part of us” is called a retrovirus. The most commonly known retrovirus is HIV, which enters our cells and changes our DNA to weaken our immune system.

Another fun fact: the human placenta (which separates a mother’s blood system from a baby) is the result of a retrovirus changing our DNA. But that’s a bit beyond the scope of this post (see sources for more information)


mRNA technology has been around for years, but never used. Why now? What has changed?

The idea of using genetic code to boost our immune system or treat cancer is definitely not new. Katalin Karikó, a Hungarian scientist, has been working on this technology since 1978.

Two issues needed to be solved for it to become viable. First, mRNA is very fragile, and it took time to figure out how to package it, so it can survive long enough to enter our cells. Secondly, the injected mRNA caused the immune system to overreact, and it counteracted the desired immune response.

However, by slowly chipping away at the problem, scientists have finally been able to perfect this technology.


What are adjuvants, and why are they added to the vaccine?

Adjuvants are used in almost all vaccines, and they trigger our immune system to produce a stronger immune response and produce more antibodies. They basically help vaccines work better. It’s like telling your immune system: “Hey, come look here. Something is going on.”

Adjuvants have been used in vaccines for more than 70 years.



This video wouldn’t be possible without the work of others. Here are the sources I’ve used during my research & script writing:

Sarda, M. (2020). The mRNA vaccines.

RNA vaccine. Wikipedia.

Chamary, J. V. (2020). Coronavirus Uses Spikes To Break Into Cells - Here’s How To Stop It.

Novel Coronavirus SARS-CoV-2. (2020). NIAID-RML.

Thaker, R. (2020). Coronavirus: B cells and T cells explained.

Susie Neilson, A. D., & Bendix, A. (2020). Moderna's groundbreaking coronavirus vaccine was designed in just 2 days.

Cuffari, B. (2020). What are Spike Proteins?

Samadani, U. (1988). 346 Days: The Race for a COVID-19 Vaccine: The Molecular Biology Behind the Fastest Vaccine Development in History.