How Do the COVID-19 mRNA Vaccines Work?

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Written by Roy E. Weiss, M.D., Ph.D.,
Chief Medical Officer for COVID-19,
University of Miami Health System

Roy Weiss

 

December 15th was a historic day.

Ninety frontline healthcare providers received their first COVID-19 vaccines. These heroes came to work every day since March, taking care of the sickest of our sick patients, making sure that we're all protected. Soon, we will all get the opportunity to protect them by also getting the COVID-19 vaccine.

But why do we need a vaccine?

The simple answer is to get rid of the virus. Infection with the virus causes a highly transmissible disease by the respiratory route and can easily be very serious. It can be transmitted by both people who have symptoms and, more importantly, people who might not even know they have COVID-19 because they are either asymptomatic or presymptomatic.

Herd immunity, where the majority of the community is protected and makes the virus less likely to spread is unlikely unless we're able to vaccinate 70% of the population. Without the vaccination, there is no such thing as herd immunity in the case of COVID-19. Failure to vaccinate the majority of the population would cause even more negative economic and human impact on our society and the world than it has already.

How an mRNA vaccine works

You may have concerns about taking the vaccine because you're unsure what's in it.

Let me explain what an mRNA vaccine is all about.

mrna
(adapted from Nature.com 2020)

In the image above, there is a little blue ball called a nanoparticle. It's a very thin ball with an outer covering of fats or lipids. Located within this structure is a tiny strand of messenger RNA. Messenger RNA is the blueprint for all the proteins that are manufactured in living things.

What happens when you receive the COVID-19 vaccine is that the specific messenger RNA encased in this little ball of lipids, this nanoparticle, gets injected into your body.  Then, the nanoparticle fuses with your cells' membranes (which are also made of lipids), and the messenger RNA is released into the cytoplasm of your cells. Once there, it instructs your cells to make a protein called the viral spike peptide, which is only present on the SARS-CoV-2 virus otherwise known as the COVID-19 virus.

All the cells in the body are primed and ready to go that and recognize “Public Enemy #1 – the virus”, "Hey guys, listen, there's a foreign substance in our body, and we need to make antibodies to fight against it, and we need to have our immune system to fight against it."

It's sort of like a boxer getting ready to fight before the match. The body’s immune cells have been primed, they know who the enemy is, so when the virus comes, the body's all ready to neutralize and destroy it because the antibodies recognize that unique protein on the surface of the virus.

This is totally safe. This protein itself does not affect the body in any way. The RNA does not affect your genes.  And, the vaccine cannot give you COVID-19. It just utilizes the machinery in your cells to make the antigen necessary to stimulate the immune system.

Pfizer or Moderna?

Two messenger RNA vaccines have been granted a EUA or an emergency use authorization by the US Federal Drug Administration – one developed by Pfizer/BioNTech and another by Moderna. Both of these vaccines are administered in two doses. There isn't much difference between the two except the Pfizer second injection is given 21 days after the first, and the Moderna is given 28 days after the first dose.

The Pfizer Vaccine has the name:  BNT162b1 and the “antigen” the messenger RNA codes for is a trimerized SARS-Co-V2 receptor binding domain.  The Modernal Vaccine has the name mRNA1273 and coes for the spike S protein of the virus in the confirmation before it fuses with the cell.  While these vaccines are both messenger RNA vaccines they are slightly different and therefore for maximum effectiveness you can't get a Pfizer vaccine on the first dose and a Moderna vaccine on the second dose; they must be the same.

how does mrna work

Most of the adverse reactions reported in both vaccines' clinical trials are very mild, and they resolved in a few days. Not surprisingly, there was pain at the injection site. Anytime you take a needle and stick it in your arm, there's going to be a moment of pain. The companies also listed fatigue, headache, muscle pain, chills, and fever.

Do they work?

In tens of thousands of trial participants, they've only had eight confirmed cases of COVID-19 in the vaccine group compared to 162 confirmed cases of COVID-19 in the placebo or the saltwater group. The efficacy from seven days after the second dose was reported to be 95.5%.

Compared to the flu vaccine, the COVID-19 vaccine is much more efficacious than the flu vaccine is in treating the flu. It's also important to note that there were no meaningful clinical differences in the overall vaccine efficacy, whether you had one or two or more comorbidities, age, obesity, diabetes, or hypertension. It's equally efficacious for everybody.

While the vaccine is likely to start stimulating antibodies soon after injection, we don't know when the antibodies will be fully protective, and we don't know how long they will last. Therefore, please continue wearing a mask, maintaining physical distancing, and practicing good hand hygiene even after getting the vaccine. It is not a panacea until we have 70% of the community vaccinated. Yes, you'll be protected, but we need to protect the community at large as well.

The final point I want to make is that a vaccine will only work if you take it. So please, I encourage you to do so.


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