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VERIFY: How COVID-19 vaccines are made and how they work

Conventional vaccines, including most flu shots, are made by growing viruses in eggs. But the pending coronavirus vaccines are different.

INDIANAPOLIS — Promising developments involving the development of COVID-19 vaccines have been met with many questions about what’s in those vaccines and how they will work.

13News viewer Pamela Smith wrote to 13News to say: “I’m just wondering how the new vaccines are made. I can’t have a flu shot because they are incubated in eggs. If the COVID vaccines are done the same way, then the shot itself could kill me because of my allergies.”

Pamela is correct: conventional vaccines, including most flu shots, are made by growing viruses in eggs.

According to the US Centers for Disease Control and Prevention, an egg-based manufacturing process has been used for more than 70 years to make both inactivated flu shots that utilize influenza virus that has been killed and a nasal spray flu vaccine that uses live (weakened) virus. The process requires millions of chicken eggs and can take as long as six months to produce a large supply of vaccine.

The leading COVID-19 vaccines are made much differently.

Pfizer and Moderna, the two companies currently developing COVID vaccines that are likely to be the first widely available in the US, are using new vaccine technology called mRNA, which stands for "messenger ribonucleic acid."

How it works

Pfizer says its researchers have been figuring out the gene sequence of COVID-19. Instead of injecting you with a tiny piece of the virus (which is how most vaccines work), the new generation of COVID-19 vaccines rely on RNA molecules that actually send messages and provide instructions to your cells. Those instructions direct your body to produce proteins that will trigger your immune system, telling it to make antibodies that can fight coronavirus if you contract it.

If it sounds extremely high-tech and complicated, it is. But the bottom line is the leading mRNA vaccines likely to be distributed here in the United States will not expose patients to a live virus and they are not manufactured using eggs. So they should not trigger that type of allergy in folks who must avoid egg products.

More research is continuing on the COVID-19 vaccines to determine if and when the CDC will approve them for distribution. If the vaccines are determined to be safe and effective against coronavirus, mRNA could become a more popular method for producing a wide variety of vaccines in the future.