Oct. 22, 2021 -- The COVID and flu vaccines are important, and both are quite effective at preventing serious illness or death. But that’s where much of their similarities end. Here’s the science behind both.

The methodology

Two of the three COVID vaccines (Pfizer and Moderna) adopted in the United States are mRNA, or messenger RNA. The shots work by delivering molecules of antigen-encoding mRNA into immune cells, triggering an immune response. They represent nearly 20 years of research and are relatively easy to produce.

For the flu vaccine, scientists harvest the virus in eggs, inactivate it, and then purify the antigen before making it on a wide scale.

The strains they attack

One of the biggest differences between the COVID vaccine and the flu vaccine is that the COVID vaccine is effective against all the currently circulating strains of the virus. The flu shot, on the other hand, is designed to handle the strains of flu scientists determine will likely circulate each year.

How Do COVID-19 mRNA Vaccines Work?Some of the COVID-19 vaccines are known as mRNA shots. How are they different from traditional vaccines? And do they contain the real virus?189


SPEAKER: How does a COVID-19

mRNA vaccine work?

COVID vaccines are now


Some of the COVID-19 vaccines

are mRNA vaccines, but what does

this mean?

mRNA vaccines are

different from traditional


mRNA vaccines don't expose you

to any real virus instead,

they're made with messenger

Ribonucleic Acid or mRNA.

This is a type of molecule that

gives instructions to the cell

for how to make different kinds

of proteins.

mRNA molecules are

a natural part of our cells

and how our bodies work.

Researchers have been working

with mRNA vaccines

for many years.

They are made more easily

and safely in a lab

than a vaccine that uses

a virus.

Because of this they can also

be made faster.

The COVID-19 mRNA vaccines

have passed many tests in labs

and in thousands of people,

and meet strict standards

from the FDA.

So how do these vaccines work?

First, a COVID-19 mRNA vaccine

is injected into a muscle

in your upper arm.

Some muscle cells take the mRNA

instructions in the vaccine

and make a harmless piece

of a protein called

a spike protein.

This protein is found

on the outside of the SARS-CoV-2

virus that causes COVID-19.

The muscle cells then destroy

the instructions for how to make

the spike protein.

The mRNA never goes

into the nucleus of your cells

where your DNA is stored.

The newly made spike protein now

sits on the surface

of the muscle cells.

Your immune system senses

the spike protein

as a foreign threat to destroy,

it starts making antibodies

to fight anything

with that spike protein on it.

This will help your body's

immune system recognize

and fight the real virus if it

ever shows up.

It's like recognizing someone

by the hat they wear.

Your body is then

prepared to spot COVID-19

and fight it off before it grows

in your body's cells.

Fast facts to remember

about COVID-19 mRNA vaccines.

They help get your body

ready to fight off the COVID-19

virus before it makes you sick,

they don't use

any live, dead, or weak virus,

they can't give you COVID-19,

they don't affect your DNA.

Want to learn more,

go to cdc.gov to find more

information about mRNA vaccines.

You can also learn more about

how the vaccines were approved

at fda.gov.



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But given that last year’s flu season was very mild because of masking and distancing, there’s concern the 2021-22 season could be severe.

“This year, the shot is quadrivalent, which means it is designed to protect against four strains,” says Rachael Lee, MD, an infectious disease specialist and assistant professor in the University of Alabama’s Division of Infectious Diseases. “Other years, it will be trivalent.”

Side effects

Both the flu and COVID vaccines can produce side effects, but the immune response to the COVID vaccine tends to be a bit harder on the body. In either case, side effects include symptoms of the diseases, like achy muscles, soreness where you get the shot, mild fevers, headaches, and sometimes a very mild cough. Symptomatic effects from both shots generally don’t last longer than24 hours.

How long they protect you

While researchers are still learning about how long the COVID vaccines are effective, the general thinking is that they offer protection longer than the flu shot, according to Jill Ferdinands, PhD, an epidemiologist in the Influenza Division of the National Center for Immunization and Respiratory Diseases at the CDC. Research suggests that within a few months of receiving the flu shot, immunity begins to wane.

But in the near future, scientists may create flu shots using mRNA technology, bringing them on par with the COVID shots’ effectiveness. In the meantime, the most important thing to know is that you should get them both.

“The data shows that your symptoms will be much milder if you get these vaccines,” says Lee. “If you get vaccinated, it will help with public health efforts.”

This is particularly true this year, when hospitals are overwhelmed with COVID patients and experts predict the flu might make a strong return.

“Our hospitals have now learned how to manage pandemic surges,” says Lee, “but we want to prevent that going forward. The vaccines are the tools to do that.”

WebMD Health News


Rachael Lee, MD, infectious disease specialist, University of Alabama Medicine, Birmingham; assistant professor of infectious diseases, University of Alabama at Birmingham.

Jill Ferdinands, PhD, epidemiologist, Influenza Division, National Center for Immunization and Respiratory Diseases, CDC.

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