Everyday, more and more people are receiving one of the COVID-19 vaccines. As vaccination becomes more widely available, many are wondering or concerned about the potential side effects.
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
It’s important to note that vaccine side effects aren’t new or unusual. For example, it’s normal for some people to experience mild side effects like headaches, muscle aches and soreness after receiving their annual flu shot.
We talked to critical care specialist Rachel Scheraga, MD, about potential side effects, what causes them and why the vaccines are safe.
Currently, three vaccines have been given the green light for distribution:
- Pfizer/BioNTech. Given in two doses, 21 days apart. It’s approved for those 16 and older.
- Moderna. Given in two doses, 28 days apart. It’s approved for those 18 and older.
- Johnson & Johnson. Given in one, single dose. It’s approved for those 18 and older.
The vaccines have not been fully approved by the Food and Drug Administration (FDA) yet, which would allow them to be sold to hospitals and healthcare providers. But all three have been approved for emergency use authorization (EUA) by the FDA because of the current state of the pandemic.
It’s important to keep in mind that we’re still in the early stages of the process. Data on side effects continues to be collected and studied.
What are the known side effects of the vaccines?
As with many vaccines, there are some side effects, says Dr. Scheraga, but those side effects are relatively mild. The side effects have mainly been arm soreness, fatigue, muscle aches, headaches and some instances of fever and chills.
The data shows that side effects are more commonly felt after the second dose of Pfizer or Moderna’s vaccine rather than after the first dose.
With Johnson & Johnson, the most commonly reported side effects were arm soreness, headache, muscle aches and nausea. Most of the side effects occurred one to two days after vaccination.
So far, no additional widespread side effects have become known. Truly severe reactions and side effects remain rare.
What causes these side effects?
According to Dr. Scheraga, the side effects have to do with how the COVID-19 vaccines work. Both the Pfizer/BioNTech and Moderna vaccines use messenger RNA (or mRNA). The strategy has been in development for years, but this is the first time it’s been used in a distributed vaccine.
In this case, the harmless “spike” protein of the virus in the mRNA vaccine triggers the secretion of antibodies and recruitment of memory immune cells in the bloodstream. This reaction allows protection if one gets infected with the virus at a later time.
With the Johnson & Johnson vaccine, a piece of DNA from the COVID-19 spike protein is injected into an adenovirus (the kind of virus that typically causes colds). This modified adenovirus can carry the DNA segment but can’t replicate it inside the body and cause illness. The DNA causes cells to make harmless versions of the spike protein and the body creates an immune response to it.
“This activation of the immune system is what leads to some of these non-specific symptoms we’re seeing,” says Dr. Scheraga.
Do the vaccine side effects mimic COVID-19 symptoms?
Dr. Scheraga notes that there are some overlapping features between the side effects and the symptoms of COVID-19. Specifically, the fever and the muscle aches are some of the general side effects that mirror COVID-19 symptoms.
It’s important to keep an eye on the side effects you experience because it’s possible that these symptoms could be a result of COVID-19.
“It’s possible that if you contract the virus a few days before you receive your first dose, those symptoms could be indicative of COVID-19 infection instead of vaccine side effects,” Dr. Scheraga says.
But, she adds, there are a few ways to tell if it’s just the side effects or something more serious. Most times, the side effects are mild and usually fade within 24 hours. You shouldn’t feel prolonged effects from the vaccine itself.
Everyone’s reaction will be on a case-by-case basis. If you find those symptoms worsening or lingering longer than a day or two, you should contact your healthcare provider. They’ll be able to direct you on the best next steps, including, potentially, a COVID-19 test.
No, you can’t get COVID-19 from the vaccine
The COVID-19 vaccines will not give you COVID-19. You’re just getting a sequence of the protein spike of the virus. You’re not getting either an active or inactive part of coronavirus.
“You’re just getting what is needed from the virus so your immune cells can develop memory so that if you do contract COVID-19 after full vaccination, your immune system will be able to fight it off quickly so you don’t get sick,” says Dr. Scheraga.
Are there any pre-existing medical conditions that could interfere with or intensify the side effects?
One question about the vaccines has been whether or not pregnant patients would experience any additional adverse reactions. So far, that’s unknown because the initial clinical trials didn’t include pregnant recipients. However, research is ongoing.
Recent guidance developed by the Centers for Disease Control and Prevention (CDC) advises that if a pregnant patient is part of a group recommended to receive the vaccine, that patient would have the ultimate choice, but should consult with their healthcare provider first.
As with other vaccines, like a flu shot, the healthcare provider administering the vaccine will check with each recipient if they’ve experienced allergies with previous vaccines. Specifically, those reactions are generally caused by additives in the vaccine.
“Once you receive a dose, you’ll be monitored for 15 minutes, which is typically enough time to see any indication of a severe allergic reaction,” Dr. Scheraga points out.
As of now, the CDC says that patients with a history of such reactions can receive the vaccine but they should have those incidents fully assessed by a healthcare provider to determine a fuller context around those incidents.
The CDC says, “These persons may still receive vaccination, but they should be counseled about the unknown risks of developing a severe allergic reaction and balance these risks against the benefits of vaccination.”
In those instances, the CDC calls for a post-vaccination observation period of 30 minutes instead of 15 minutes.
Are the vaccines safe?
Yes, all three COVID-19 vaccines are safe and effective.
“There’s a lot of concern because of the speed of development and whether or not mRNA vaccines are a brand new platform,” says Dr. Scheraga. “But it’s not brand new technology. This platform has been under development for this kind of real-time distribution for a while and was worked on prior to the pandemic.”
The vaccines are safe, effective and potentially life-changing.