Updated Aug. 25, 2021

Millions of Americans have received COVID-19 vaccines developed by Pfizer-BioNTech, Moderna, and Johnson & Johnson/Janssen (J&J). Americans 12 and older are eligible for the vaccine as of May 2021.

Both the Pfizer and Moderna vaccines require two doses to be fully effective. The J&J vaccine currently requires one dose.

You may be familiar with other vaccines. However, you should follow certain steps after receiving the COVID-19 vaccine.

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Does the COVID-19 Vaccine Have Side Effects?

Reported data from the vaccines’ clinical trials show they are safe and effective. Serious side effects are rare.

When you receive the vaccine, you will be monitored for an allergic reaction for 15 to 30 minutes after injection. Allergic reactions to the vaccine are rare.

The most common side effects to the vaccine include:

  • Injection site pain/redness/swelling
  • Arm soreness
  • Fatigue
  • Fever or feverishness
  • Chills
  • Body/joint/muscle aches
  • Headaches

If you have side effects, you can use ibuprofen or acetaminophen as recommended by your care provider. If you have a sore arm, apply an ice pack to ease the discomfort.

According to the Centers for Disease Control and Prevention (CDC), you should contact your doctor if pain or redness at the injection site increases after 24 hours. You should also contact your doctor if your symptoms aren’t going away after a few days.

In rare cases, some people who received the J&J vaccine developed a rare, serious blood clot. The FDA and CDC temporarily paused the distribution of the vaccine to investigate the blood clot cases.

After investigation, the FDA and CDC determined the vaccine’s benefits in preventing COVID-19 outweigh its risks in people 18 and older. These adverse effects are extremely rare.

The J&J vaccine is safe and effective in preventing COVID-19. If you or a loved one receives the J&J vaccine, you DO NOT have to take any medications to prevent blood clots. Call your doctor if you experience side effects related to blood clots, including:

  • Shortness of breath
  • Chest pain
  • Leg swelling
  • Persistent abdominal pain
  • Severe headaches or blurred vision
  • Easy bruising or tiny blood spots under your skin, beyond the injection site

The reported adverse effects associated with the J&J vaccine have not been linked to the Moderna or Pfizer vaccines.

“Most people, regardless of the vaccine they receive, should not expect severe side effects like this,” says Donald Yealy, MD, chief medical officer, UPMC. “It’s exceptionally rare.”

The Centers for Disease Control and Prevention (CDC) is monitoring reports of the heart conditions myocarditis and pericarditis in people who received the Moderna and Pfizer vaccines, especially adolescents and young adults.

According to the CDC, the reported cases were rare and happened mostly in male adolescents and young adults 16 and older. Symptoms usually presented within days of vaccination, and patients typically responded well to rest and medications.

The CDC continues to recommend vaccination for Americans 12 and older.

Do You Still Need to Wear a Mask After Getting the COVID-19 Vaccine?

Like any vaccine, it takes time for your body to build up protection after vaccination. The COVID-19 vaccine’s full potency doesn’t take effect until after the second dose.

According to reported data from the Pfizer and Moderna vaccines, both are at least 94% effective in preventing symptomatic COVID-19. The J&J vaccine is about 70% effective in preventing mild to moderate COVID-19 and 85% in preventing severe illness.

It is still possible to get COVID-19 after being vaccinated.

It is also not yet known how well a COVID-19 vaccine will prevent you from spreading the coronavirus to other people.

You should continue to follow CDC public health guidelines, including wearing a mask, social distancing, and maintaining hand hygiene after getting vaccinated.

Once you are fully vaccinated, you can resume many activities without wearing a mask or physically distancing, according to the CDC. You should continue to follow existing laws or regulations about masking, including business guidelines.

You are considered fully vaccinated if at least two weeks have passed since you received the second dose of the Moderna or Pfizer vaccines, or if at least two weeks have passed since you received the J&J vaccine.

There are still some situations where you should continue to wear a mask, even once fully vaccinated. Those include travel and health care settings.

When Do I Get the Second Dose of the COVID-19 Vaccine?

You should get the second dose at least 21 days (for Pfizer-BioNTech) or at least 28 days (for Moderna) after your first dose.

If the second dose is delayed beyond 21 or 28 days, it will still be effective. The CDC says you can get the second dose of the Pfizer and Moderna vaccines up to 42 days after the first dose.

When you get your first dose of the Pfizer or Moderna vaccine, talk to your health provider about scheduling the second dose.

Where Can I Go for COVID-19 Vaccine Information?

For information about COVID-19 vaccination at UPMC, visit

Use the CDC’s “v-safe” smartphone tool to report side effects or other concerns to the CDC; someone may contact you for more information. The tool also will remind you to get the second dose of the vaccine. Visit to register.


Centers for Disease Control and Prevention, What to Expect After Getting a COVID-19 Vaccine. Link

About UPMC

Headquartered in Pittsburgh, UPMC is a world-renowned health care provider and insurer. We operate 40 hospitals and 700 doctors’ offices and outpatient centers, with locations in central and western Pennsylvania, Maryland, New York, and internationally. We employ 4,900 physicians, and we are leaders in clinical care, groundbreaking research, and treatment breakthroughs. U.S. News & World Report consistently ranks UPMC Presbyterian Shadyside as one of the nation’s best hospitals in many specialties and ranks UPMC Children’s Hospital of Pittsburgh on its Honor Roll of America’s Best Children’s Hospitals.