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COVID-19 Vaccine: How mRNA Vaccines Work


Both the Pfizer and Moderna COVID-19 vaccine are made from what is called messenger RNA or mRNA.

To trigger an immune response, many vaccines put a weakened or inactivated germ into our bodies. That protein then fights off the virus.

That’s not the case with theses COVID vaccines.

The mRNA vaccines teach the cells in our bodies how to a make a protein and that protein triggers an immune response in our bodies.

Dr. Paul Offit is the Director of the Vaccine Education Center at the Children’s Hospital of Philadelphia.

He’s also on the vaccine committee that gives recommendations to the FDA.

Dr. Offit says while this is the first time an mRNA vaccine has been put into use for the general public it’s not a new concept.

“It’s not a novel molecule. It’s not something we have seen before. We all have messenger RNA’s in our bodies. And frankly it’s not a novel strategy,” said Dr. Offit. “This particular notion using messenger RNA as a vaccine has been around for 20 years. People have been working on messenger RNA vaccines against human immunodeficiency virus, malaria, tuberculosis, Ebola, zika, etc. so this is just the first one to get above the water to become a commercial product.”

Both Pfizer and Moderna’s vaccines require two doses.

The Pfizer vaccine needs 21 days between doses. The Moderna vaccine was tested with 28 days between doses.

Your body will start building up an immune response after the first dose, but a second dose will increase your protection dramatically.

It also increases the amount of memory cells you produce which plays a role in how long immunity from the vaccine lasts.

“It looks like you have very high frequency of memory cells. That’s a great sign. When you look at antibodies, you’re looking at just the tip of the iceberg,” said Dr. Offit. “If you look below the tip of the iceberg, you’re looking at memory cells and if you can have relatively high frequency of memory cells that really tells you’re going to have relatively longer live immunity.”

It’s not yet known how long immunity from any of the vaccines will last.

The Pfizer vaccine has been approved by the FDA. The Moderna vaccine will likely be approved by the end of this week.

Katie Thoresen is WXPR's News Director/Vice President.
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