Shared from the 1/24/2021 Philadelphia Inquirer - Philly Edition eEdition

The science behind the shot

Here is a step-by-step guide to what happens when you receive a COVID-19 vaccine. It is biologically impossible for the RNA vaccines to cause infection. And the RNA never comes into contact with your DNA.

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Illustrations by DOMINIQUE DeMOE / Staff Artist

RNA Blueprint

1. presses The person the administering syringe into the the recipient shot de ’s - arm, injecting billions of tiny spheres made of waxy molecules called lipids. Each one contains several copies of the

RNA blueprint for making the spike on a coronavirus particle.

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In the lymph nodes, immune-system cells respond by making antibodies: little Y-shaped proteins that are customized to latch onto the virus spike. If the person is ever exposed to an actual virus, the antibodies latch onto its spikes so that it cannot penetrate a cell — like putting gum on a key so it cannot penetrate a lock. Some antibodies remain in the bloodstream, ready to serve as first responders. In addition, specialized cells form a memory of the spike, retaining the ability to make more antibodies and other defenses in a hurry.

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The cell then “presents” the spike proteins on its surface and travels to the lymph nodes. Though the proteins cannot cause an infection, they are recognized by the immune system as a foreign presence.

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When the lipid spheres come into contact with white blood cells in the person’s arm, they deposit their cargo inside. The RNA travels across the cell membrane into the gel-like cytoplasm. It does not enter the cell nucleus, where DNA is located, so it does not have any affect on the person’s genetic code.

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The RNA molecules are fed through roundish, machine-like structures called ribosomes, a type of cellular assembly line where proteins are made. In an infected person, viruses hijack this machinery to make copies of themselves. But in the vaccines, the RNA contains the recipe only for the exterior “spikes” of a virus particle, not an entire virus. They cannot cause an infection.

The first two COVID-19 vaccines to be distributed, one made by Pfizer Inc. and BioNTech SE, the other by Moderna Inc., are the first such drugs to consist of genetic instructions in the form of RNA: ribonucleic acid.

Cells in the arm use this blueprint to make harmless fragments of the coronavirus, prompting the immune system to make antibodies and other customized defenses should the person ever be exposed to the actual virus.

Both prevented more than 94% of infections in clinical trials. Some recipients experience a temporary fever, arm pain, or headache, but there is no evidence of any longterm complications.

Here is a step-by-step description of the process, written with guidance from University of Pennsylvania scientist Drew Weissman, whose work with former colleague Katalin Karikó, now at BioNTech, helped make the vaccines possible. tavril@inquirer.com

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