COVID-19 vaccine and booster side effects: What to expect after your shot

If you're due for your first, second or third shot of any COVID-19 vaccine, you may be wondering what side effects to expect. Here's what you should know.

Kim Wong-Shing Former Senior Associate Editor / Wellness
During her time at CNET, Kim Wong-Shing loved demystifying the world of wellness to make it accessible to any reader. She was also passionate about exploring the intersections of health, history and culture. Prior to joining CNET, she contributed stories to Glamour, MindBodyGreen, Greatist and other publications.
Expertise Nutrition | Personal care | Mental health | LGBTQ+ health Credentials
  • Reads health studies in her sleep.
Amanda Capritto
Kim Wong-Shing
6 min read
Sarah Tew/CNET

As COVID-19 cases surge across the US, the vast majority of hospitalizations and deaths continue to be in unvaccinated people. And thanks to the omicron variant, staying up to date on your COVID-19 vaccinations, including booster doses, is incredibly important. Omicron's high number of mutations allow it to evade some immunity, so that a two-dose series of Moderna or Pfizer is now only about 35% effective against infection, per a Centers for Disease Control and Prevention statement in December. But a booster dose restores protection to around 75%.

The CDC now recommends booster doses for all adults ages 18 and older, as well as children ages 12 and up who received Pfizer. You should wait two to five months after being fully vaccinated before getting your booster, depending on which vaccine you received (two months for Johnson & Johnson, five for Pfizer or Moderna).

Still, vaccine fears and myths abound. Stories about side effects (fake or not) may make some people more hesitant to get the shot. There are tens of millions of people in the US who are eligible for the vaccine but have yet to receive it, who now face pressure from federal mandates, city policies and more.

And even if you're fully vaccinated, you may hesitate to get your booster, especially if you experienced uncomfortable side effects with your first or second shot.

So which side effects can you expect, either from a booster or initial shots? Here's what to expect if you get a COVID-19 vaccine or booster, whether it's the Pfizer, Moderna or Johnson & Johnson version -- and how you can report side effects to the CDC.

Read more: Which COVID booster shot should you get?

Mark Lennihan/Getty Images

Common COVID-19 vaccine side effects

According to the Centers for Disease Control and Prevention, common COVID-19 vaccine side effects include

  • Injection site pain
  • Injection site swelling
  • Fever
  • Chills
  • Headache
  • Tiredness
  • Nausea
  • Muscle pain

Other side effects that have been reported in both Moderna and Pfizer include swollen lymph nodes, vomiting and joint pain. In general, most people report worse side effects after the second dose of the Pfizer and Moderna vaccines, both of which are two-shot mRNA vaccinations, than the first. These effects should go away within a few days.

Johnson & Johnson vaccine side effects

The Johnson & Johnson vaccine only requires one dose as opposed to the two doses required for the Pfizer and Moderna vaccines. As of December, the CDC recommends that people get Moderna or Pfizer instead of J&J. That's because of one exceedingly rare, but serious side effect associated with J&J: blood clots. The risk of blood clots is highest, though still very rare, in women under 50. 

Still, the J&J vaccine is available for those who need or prefer it. According to the FDA, the most commonly reported side effects of the Janssen vaccine are headaches, nausea, fatigue, muscle aches and injection site soreness. Most people experienced these side effects in the one to two days following injection.

Oxford-AstraZeneca vaccine side effects

Similar to Johnson & Johnson, AstraZeneca is a viral vector vaccine, but it requires two doses instead of one. AstraZeneca has not been approved in the US, but remains in use in much of the rest of the world.

Also similar to J&J, blood clots are also a very rare but serious side effect of the AstraZeneca vaccine. It was temporarily discontinued in several countries, but remains approved by the European Medicines Agency and World Health Organization and is available in countries such as Canada. 

According to the Government of Canada, common side effects from AstraZeneca are similar to those of other vaccines: redness, soreness or swelling at the injection site, chills, fatigue, joint pain, headache, mild fever and muscle pain.

Sarah Tew/CNET

COVID booster side effects

The commonly reported side effects of a COVID vaccine booster are similar to those for the primary vaccinations, according to the CDC and US Food and Drug Administration. These effects include:

  • Fever
  • Pain at the injection site
  • Fatigue
  • Headache
  • Muscle aches
  • Chills

Most side effects are mild to moderate, and resolve within one or two days.

Why do vaccines cause side effects?

All vaccines have possible side effects with mild to moderate severity. Typical vaccine side effects include local pain, swelling, redness and sometimes bruising at the injection site, as well as fever and tiredness, says Dr. Roshni Mathew, pediatric infectious diseases physician at Stanford Children's Health

With any vaccination, you can expect a bit of pain during and after the injection, says Dr. Thomas Duszynski, director of epidemiology education at Indiana University. He adds that some people may experience chills, fatigue or minor headaches after vaccines. 

Side effects like fever, chills and fatigue after a vaccination indicate that your immune system is responding to the vaccine, Duszynski says. "Even if you don't experience these [side effects], it does not mean that your immune system isn't working; it is just working a little more quietly," he says. 

As for bruising, swelling and sensitivity at the injection site, well, your body would likely respond similarly after a needle punctured your skin for any other purpose. These side effects can occur after any vaccine, as well as when people get blood drawn or receive steroid shots or vitamin injections.

Watch this: Stanford expert's bottom line on what a COVID vaccine means for you

Which side effects are cause for concern?

Severe side effects from the COVID-19 vaccines are extremely rare, according to the CDC and FDA. However, that doesn't mean they're not possible, regardless of which vaccine you get and whether it's a booster or initial dose. Some of the rare, yet severe side effects of the COVID-19 vaccines include:

  • Myocarditis, or inflammation of the heart muscle
  • Pericarditis, or inflammation of the lining of the heart

J&J and AstraZeneca also come with a few additional risks of severe side effects: blood clots, a platelet disorder called Immune Thrombocytopenia and a neurological disorder called Guillain Barré. 

If you experience any of the following symptoms after your shot, seek medical attention immediately:

  • Chest pain
  • Shortness of breath, or difficulty breathing
  • A fast-beating, fluttering or pounding heart
  • Swelling of the face or throat
  • A bad rash all over the body
  • Dizziness and weakness
  • Leg swelling or pain
  • Persistent stomach pain
  • Easy bruising
  • Unusual or excessive bleeding
  • Difficulty walking, speaking or moving your face
  • Difficulty controlling your bladder or bowels
  • Double vision

Allergic reactions

It's possible to have an allergic reaction to a vaccine. Although severe allergic reactions are likely to be rare, "It would be important for individuals with known allergies to speak with their health care provider prior to receiving the vaccine," Duszynski says. The CDC recommends a thorough risk assessment and potential deferral of the vaccine for people with a history of severe allergies to other vaccines, and avoidance of vaccination by people with a history of severe allergies to any ingredients in the COVID-19 vaccines.

Most allergic reactions occur within a few minutes to an hour after the shot, which is why your provider will likely ask you to stay for monitoring after your vaccination.

Sarah Tew/CNET

How long do vaccine side effects last?

Vaccine side effects typically don't last longer than a couple of days, Mathew says. Some people may experience side effects for several days. Side effects that were related directly to the injection site, like bruising and redness, should subside relatively quickly, while whole-body side effects like fever and headache may last longer.

If you're still having side effects a week or more after you get a vaccine -- COVID-19 or otherwise -- call your doctor or go to urgent care. If you feel the effects are life-threatening (like a severe allergic reaction), seek emergency medical care right away.

Are there long-term side effects from any of the COVID-19 vaccines? 

At this point, it's too early to determine whether the COVID-19 vaccines are capable of causing long-term side effects, but experts are confident the vaccines are safe. The CDC, WHO, FDA and other health institutions will continue to monitor long-term effects and collect data as more people get vaccinated.

How to report COVID-19 vaccine side effects

The CDC has a tool that allows people who have received one or two doses of any COVID-19 vaccine to track and report side effects. The tool, called V-Safe After Vaccination Health Checker, uses messaging and survey functions to automatically check in on people after they get vaccinated. You can sign up for V-Safe on your smartphone after getting the vaccine. You'll need your vaccine info handy, including which type of vaccine you received and the date and time you received it. Using the chat function, you can tell the tool your side effects. Someone from the CDC may call you and ask for more information if you report severe or unusual side effects.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.