Updated June 18, 2021

In December 2020, the FDA granted emergency use authorization (EUA) to two COVID-19 vaccines. The distribution of those vaccines began nationwide later that month.

Pfizer-BioNTech and Moderna developed the two vaccines, which both use mRNA to help your body learn how to fight the coronavirus.

The Pfizer and Moderna vaccines have a lot in common. One similarity is that both require two doses received weeks apart. A third vaccine, developed by Johnson & Johnson/Janssen, currently requires only one dose.

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Why Are There Two Doses of the Moderna and Pfizer Vaccines?

Clinical trial data reported that both the Moderna and Pfizer vaccines are about 95% effective in preventing symptomatic COVID-19.

The vaccines begin to provoke an immune response after the first dose. However, they do not become fully effective until after the second dose.

Because of that, while one dose will provide some level of protection, you will need both doses for full protection.

According to the FDA, using one dose or less than the dosage used in the clinical trials would be “concerning.”

When Should I Get the Second Dose of the Moderna and Pfizer Vaccines?

If you received the Moderna or Pfizer vaccines, you will need to wait a certain length of time for the second dose:

  • If you received the Pfizer vaccine, you should wait a minimum of 21 days for the second dose.
  • If you received the Moderna vaccine, you should wait a minimum of 28 days for the second dose.

The CDC says you should get your second dose as closely to the recommended date as possible. However, if you can’t get your second dose exactly on the recommended date, the vaccine will still be effective. You can receive the second dose up to 42 days after the first dose, according to the CDC.

“Don’t worry if you can’t get your second dose exactly 21 or 28 days after your first dose,” says Graham Snyder, MD, medical director, Infection Prevention and Hospital Epidemiology, UPMC. “If you have to delay the second dose, it will still be effective up to six weeks after the first dose.”

Where Should I Get the Second Dose of the COVID-19 Vaccine?

You should receive the second dose of the Moderna or Pfizer vaccine from the same provider where you got the first dose.

When you receive the first dose of the vaccine, talk to the provider about scheduling an appointment for the next dose.

UPMC is offering second-dose vaccine appointments even if you did not receive your first dose at UPMC. But we still encourage you to go to the location where you received your first dose.

If you do want to have your second dose at UPMC, visit or call 844-UPMCVAC (844-876-2822) between 8 a.m. and 5 p.m., seven days a week.

  • If you schedule online, there is an option to indicate that this will be your second dose. Have your vaccine card handy.
  • If you schedule by phone, say that this is your second dose and that you did not get your first dose at UPMC. 

Do I Have to Wear a Facemask After Getting the Second Dose of the COVID-19 Vaccine?

You should continue to wear a facemask until two weeks after your second dose of the vaccine.

Once two weeks pass after your second dose, you are considered fully vaccinated. According to the CDC, once you are fully vaccinated, you can resume many activities without wearing a mask or physically distancing. You should continue to follow any existing laws or regulations about masking, including business guidelines.

Before those two weeks pass, you should continue to follow masking and other COVID-19 prevention methods. Wearing a cloth facemask in public and when around people not from your household can protect you and others:

  • It takes time for the vaccine to trigger your immune system response.
  • While the vaccine is highly effective in preventing symptomatic COVID-19, it is not 100% effective.
  • You could still be contagious. You could spread COVID-19 to others, even if you don’t get sick yourself.

For more information about the COVID-19 vaccine, visit


Centers for Disease Control and Prevention, Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines Currently Authorized in the United States. Link

Food and Drug Administration, FDA Statement on Following the Authorized Dosing Schedules for COVID-19 Vaccines. 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.