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Side Effects From COVID-19 Vaccine: A Sign That They're Working

Close up of a doctor giving a vaccination in the right arm of a patient.
Close up of a Doctor making a vaccination in the shoulder of a patient.

Getting your COVID-19 vaccine may come as a relief, but for some, it also can come with some side effects — like those reports of late of a red ring or rash on your arm after the shot, for instance.

Dr. Joseph Chang, Chief Medical Officer of Parkland Health and Hospital System explains to KERA's Sam Baker why the side effects usually aren't cause for worry.


What Causes The Side Effects?

The side effects that we see are pretty much due to your own body's immune response to the vaccine. Actually, if you have those side effects, like fever, body aches, some tiredness, and fatigue - like even the red rash on your arm - it's actually a sign that your body is reacting to the viral particles and making antibodies. So that's actually a really good sign.

How Does That Work?

The vaccine goes into your body, the mRNA , and it goes into your cells and your cells take that messenger RNA and start to produce what's called a spike protein.

As the cells make that protein, your body recognizes that as, “Hey, that's not me.” And so anything that's not “me,” your immune system will react against and then produce a whole lot of antibodies and other sorts of immune proteins against it. And that's what you're feeling in your body.

So that's good because that's how the body remembers how to fight that virus, if it actually sees the real thing.

If You Don't Get Side Effects, Does That Mean The Vaccine’s Not Working?

We know from the 40,000-person study that both Pfizer and Madrona did that up to 50% to 60% of those patients will have some sort of reaction. We know the vaccine is over 95% effective. So that means that 47% of those people didn't feel a thing, yet it was still very effective. So not getting symptoms means you're just in the lucky half that didn't end up having any reaction.

Side Effects That Are Cause For Concern

One reaction is what we call anaphylaxis or severe allergic reaction. Those are reactions we see within the first 15 to 20 minutes after receiving the vaccine in the observation areas of Parkland sites and all reputable sites.

At Parkland, we suggest that if you have a history of being allergic to anything, we want to watch you for about 30 minutes before we let you go. Just for a little extra precaution.

The county sites, your doctor's office, and the major hospital systems have prepared emergency treatment and personnel who are trained to treat severe allergic reactions.

What About Pharmacies Who Offer The Vaccine?

I would call that pharmacy beforehand and make sure they have the ability and the personnel available to take care of severe allergic reactions.

Are You Worried That Side Effects Could Cause People Already Skeptical About The Vaccine To Stay Away?

That's really our biggest concern. Surveys now show about 60% of folks in Dallas are willing to immediately get the vaccine whenever it's available or are strongly considering getting it. Lump those together and that still leaves about 40% to 45% of folks who are skeptical or have said, they're not going to get the shot.

Compare that to the number needed for herd immunity, 70 to 80%, with a number of folks that are positive on the vaccine, and they don't quite match. So, we still have a ways to go.

And so it does worry me, especially the misinformation that's out there, scaring folks. At Parkland, we’re helping with the county’s efforts to get good information out there so people can make a good decision.


The Second COVID-19 Shot Is a Rude Reawakening for Immune Cells

What the Vaccine’s Side Effects Feel Like

CDC: Allergic Reactions Including Anaphylaxis After Receipt of the First Dose of Pfizer-BioNTech COVID-19 Vaccine

Interview highlights were lightly edited for clarity.

Got a tip? Email Sam Baker at You can follow Sam on Twitter @srbkera.

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