Search IconSearch

If You Don’t Get Sick After Your COVID-19 Vaccination, Does It Mean Your Immune System Isn’t Working?

Get the short answer from an inflammation and immunity specialist

A woman wearing pajamas sitting in bed with her eyes closed, holding her head like she's in pain

Q: According to the CDC, common side effects of COVID-19 vaccinations include fever, chills, tiredness and headache, in addition to pain or swelling in the arm where the shot was administered. Some say these side effects are good because they prove that your immune system is working. But if you don’t experience any symptoms, does that mean the vaccine, or your immune system, isn’t working?


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

A: Everyone’s hearing about side effects with the COVID-19 vaccines, especially the second dose of Moderna’s and Pfizer’s vaccines. So, people are worried.

But when you actually look at the statistics from the trials, most people didn’t have side effects. A little over 50% didn’t experience any side effects at all and remember, they were still 94% protected after receiving the vaccine. So, you don’t need to worry if you don’t have any symptoms after your COVID-19 vaccinations.

Another thing that helps is knowing what’s going on in your body after you get the vaccine. When you get the messenger RNA vaccine, little lipid droplets that have mRNA in them get essentially taken up by cells in your arm muscle. The cells start making a spike protein, so your body thinks your muscle cells are massively infected with the coronavirus. Because of this, your body will try to fight off the simulated infection in the cells. That’s what causes some of the inflammation that people experience.

Then, those cells that have replicated the COVID-19 spike protein (RNA) get overtaken by immune cells that can communicate with the cells that make antibodies.

Through this exchange, antibodies specific for SARS-CoV2 are generated. This process takes place in your adaptive immune system. Your innate immune system is the one that locates an infection and attacks it. That’s what can cause sore arms, fevers or muscle aches — your innate immune system going kind of crazy.

Vaccines are so valuable because they help correct that imbalance during an actual infection. So people who have trouble making antibodies quickly enough can make them more effectively after getting the vaccine.

With so many people getting vaccinated, the medical community is very interested in why some people experience all the symptoms while others don’t. They’re still in the process of sorting this all out. Right now, we don’t understand it. But we do know that the two main vaccines that have been approved for emergency use are effective whether or not you’ve developed side effects — and you don’t have to feel terrible to prove that you’re protected from COVID-19.

Thaddeus Stappenbeck, MD, PhD, Chairman of the Department of Inflammation and Immunity at Cleveland Clinic’s Lerner Research Institute.


Learn more about our editorial process.

Related Articles

Healthcare provider placing bandaid on upper arm after a shot
June 5, 2024/Infectious Disease
Are You Up to Date on Your COVID-19 Vaccines?

Updated vaccinations are recommended to better protect against the evolving virus

Person coughing into a tissue by window during sunny, summer day
June 4, 2024/Primary Care
Summer Sniffles: Winter Isn’t the Only Time You Can Catch a Cold

Enteroviruses are often to blame for summer colds, leading to a runny nose, sore throat and digestive symptoms

Red inflammation on an upper arm
May 30, 2024/Infectious Disease
Should You Be Worried About COVID Arm?

Redness, swelling, itching and rash can happen when your body’s immune system reacts to the vaccine injection

Arrivals at a busy airport
May 28, 2024/Infectious Disease
What Is Asymptomatic COVID-19 and Are You Contagious?

Studies suggest 1 in 5 people infected with the coronavirus never develop symptoms

blood clot inside an artery
April 26, 2024/Infectious Disease
The Connection Between COVID-19 and Blood Clots

An increased risk of blood clots can last for nearly a year after a COVID-19 diagnosis

Masked healthcare provider with vaccine and science icons floating around for immunocompromised
If Your Immune System Is Compromised, Can You Get Vaccinated?

The answer varies from person to person and vaccine to vaccine

Person getting an audiogram, with technician
April 1, 2024/Ear, Nose & Throat
The Link Between COVID-19 and Tinnitus (That Ringing in Your Ears)

COVID-19 may be associated with tinnitus, but research is still ongoing

aerial view over crowd of commuters
March 18, 2024/Infectious Disease
How Does COVID Immunity Work?

The short answer: It’s complicated, but the basic care precautions still prevail, like washing your hands and isolating if you’re sick

Trending Topics

Female and friend jogging outside
How To Increase Your Metabolism for Weight Loss

Focus on your body’s metabolic set point by eating healthy foods, making exercise a part of your routine and reducing stress

stovetop with stainless steel cookware and glassware
5 Ways Forever Chemicals (PFAS) May Affect Your Health

PFAS chemicals may make life easier — but they aren’t always so easy on the human body

jar of rice water and brush, with rice scattered around table
Could Rice Water Be the Secret To Healthier Hair?

While there’s little risk in trying this hair care treatment, there isn’t much science to back up the claims