Why Does the COVID-19 Vaccine Cause a Sore Arm?

The COVID-19 vaccine can cause some commonly known side effects. One of the most commonly discussed side effects is a sore arm at the injection site.

You may have heard people who've been vaccinated against COVID-19 say they couldn't comfortably move their arm for a day or two after their shot. Many people have taken to social media to share their experience with this uncomfortable—yet harmless—symptom.

But why does your arm get sore after the COVID-19 vaccine? It’s a little more complicated than most people realize. Read on to learn more about why some people have a sore arm after being vaccinated and what you can do about it.

Common COVID-19 Vaccine Side Effects

Side effects from the COVID-19 vaccine are normal signs that your immune system is doing its job, according to the Centers for Disease Control and Prevention (CDC). The side effects from the shot may affect your ability to do some activities. But they should last no more than a few days.

The most common side effects from the COVID-19 vaccine include:

• Pain in the arm where you got the shot
• Redness in the arm where you got the shot
• Swelling in the arm where you got the shot
• Tiredness
• Headache
• Muscle pain
• Chills
• Fever
• Nausea

Side effects after your second shot may be more intense than after the first. But they are normal signs that your immune system is hard at work.

Why the COVID-19 Vaccine Can Cause a Sore Arm

The COVID-19 vaccine is an intramuscular injection. This means it’s injected into the muscle. It’s recommended that it be injected into the deltoid muscle in the arm. The deltoid is the large muscle that gives the shoulder its range of motion.

There are a few reasons why this can cause arm soreness.

“The vaccine can trigger inflammation at the site of the injection, which suggests the vaccine is starting to activate your immunity,” Isabel Valdez, PA-C, physician assistant and assistant professor of general internal medicine at Baylor College of Medicine, tells Verywell. There is also a “tiny injury” to the muscle where the needle is injected, she says.

Your body’s immune reaction may also cause a sore arm, infectious disease expert Aline M. Holmes, DNP, RN, a clinical associate professor at Rutgers University School of Nursing, tells Verywell.

“Your immune system uses several mechanisms to fight off infections," she says. "We all have macrophages, B-lymphocytes, and T-lymphocytes as part of our white blood cells."

Macrophages work to break down viruses, bacteria, and dead or dying cells, Holmes explains. B-lymphocytes produce antibodies that attack pieces of the virus left behind by the macrophages. And T-lymphocytes attack cells in the body that have been infected. 

The COVID-19 vaccines “trick the body's immune system to think it's being invaded by the virus,” according to Holmes. As a result, your body sends white blood cells to fend off the “intruder.”

“Think of your arm as being the battlefield where your white blood cells and the vaccine components are at war,” Holmes says. “All the time, the body’s B-lymphocytes are making antibodies.”

Why Does Soreness Last For a Few Days?

Your body's process of reacting to the vaccine can take several days. which is why you may end up having arm soreness for that time, Holmes says. The pain from the inflammation caused by the shot itself also takes time to go away.

“Think of inflammation as the pain you get after you hurt your knee or ankle; that kind of pain can take a few days to resolve,” Valdez say. She also adds that the small injury to your muscle from the needle also takes time to heal. “The site of injection is [the] starting block of the immune response. A lot is going on in that one site.”

How to Treat a Sore Arm After Your Shot

As stated before, if you have a sore arm after your COVID-19 vaccine, it should only last for a few days. But If you’re uncomfortable, there are a few things you can do to help:

• Move your arm after your shot. Using your arm and making a point to move it often after you’ve been vaccinated stimulates blood flow to the area. It can also help reduce soreness, according to Richard Watkins, MD. Dr. Watkins is an infectious disease specialist and a professor of internal medicine at the Northeast Ohio Medical University.
• Try a cool compress. Applying a clean, cool, wet washcloth over the area may help reduce soreness, Valdez says. “This may bring down the inflammation, much like when you ice your knees after exercise or injury,” she says.
• Continue using your arm. It can be tough if you’re uncomfortable, but stretching and continuing to use your arm can help minimize or reduce soreness, Watkins says.

The CDC recommends talking to your doctor about taking over-the-counter medicines, like ibuprofen, acetaminophen, aspirin, or antihistamines, for arm soreness and other post-vaccination pain. Do not take these medications if you have any condition that would normally prevent you from taking them.

Summary

A sore arm is a common side effect of the COVID-19 vaccine. It's a sign that your body's immune system is responding as it should. Though it may last a few days, using cool compresses, taking over-the-counter medications, and keeping your arm in motion can make you feel more comfortable. It can also make the soreness go away.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.