COVID-19 Vaccines: Pfizer vs. Moderna – What’s the Difference?

PFIZER VS. MODERNA – What’s the Difference?

There are lots of questions about the differences, or similarities, between the Pfizer and Moderna COVID-19 vaccines. Memorial Healthcare is bringing you the following Frequently Asked Questions to help provide you with answers to those questions.

How do COVID-19 vaccines work?

According to the CDC, “COVID-19 vaccines help our bodies develop immunity to the virus that causes COVID-19 without us having to get the illness. Different types of vaccines work in different ways to offer protection, but with all types of vaccines, the body is left with a supply of ‘memory’ T-lymphocytes as well as B-lymphocytes that will remember how to fight that virus in the future.”

Can I get COVID-19 from the vaccine?

No. None of the authorized and recommended COVID-19 vaccines or vaccines currently in development in the United States contain the live virus that causes COVID-19. This means that a COVID-19 vaccine cannot make you sick with COVID-19.

Can I still get COVID-19 after the vaccine?

It typically takes a few weeks for the body to produce T-lymphocytes and B-lymphocytes after vaccination. Therefore, it is possible that a person could be infected with the virus that causes COVID-19 just before or just after vaccination and then get sick because the vaccine did not have enough time to provide protection.

What is Emergency Use Authorization (EUA)?

On December 11, 2020, the FDA issued an Emergency Use Authorization (EUA) for the use of the Pfizer-BioNTech COVID-19 vaccine. On December 18, 2020, the FDA issued an EUA for the use of the Moderna COVID-19 vaccine. The issuance of an EUA is different than an FDA approval (licensure) of a vaccine.

In determining whether to issue an EUA for a product, the FDA evaluates the available evidence and assesses any known or potential risks and any known or potential benefits. And if the benefit-risk assessment is favorable, the product is made available during the public health emergency. Once a manufacturer submits an EUA request for a COVID-19 vaccine, the FDA then evaluates the request and determines whether the relevant statutory criteria are met, considering the totality of the scientific evidence about the vaccine that is available to the agency.

How old do I have to be to get the COVID-19 vaccine?

The Pfizer emergency use authorization (EUA) is for those ages 16 and older. The Moderna vaccine is for those ages 18 and older, although the company recently began testing its vaccine in 12- to 17-year-olds.

The CDC states that children and adolescents outside of these authorized age groups should not receive COVID-19 vaccinations at this time.

How is the vaccine given?

Both vaccines are given in the muscle of the upper arm.

How effective is the vaccine?

Pfizer showed efficacy of 95% at preventing symptomatic COVID infection. The Moderna vaccine was 94.1% effective.

How long before I’m protected?

The Pfizer vaccine was measured starting from seven days after the second dose. The Moderna vaccine was measured starting from 14 days after the second dose.

Does the vaccine work in all people?

Yes, both vaccines appeared to have high effectiveness in clinical trials among people of diverse age, sex, race, and ethnicity categories and among persons with underlying medical conditions.

Why do I need two shots?

The first dose is a priming dose, followed by a booster shot. Moderna doses are 28 days apart and the Pfizer vaccine is 21 days apart. Second doses administered within a grace period of four days earlier than the recommended date for the second dose are still considered valid per the CDC.

Can I get a Pfizer and Moderna vaccine?

No, you must receive first and second doses by the same manufacturer.

What are the most common side effects?

The most common side effects of both vaccines are injection site pain, fatigue, headache, muscle pain and joint pain. Some people in the clinical trials have also reported fever.

Side effects are more common after the second dose; younger adults, who have a more robust immune systems, reported more side effects than older adults.

Do side effects mean the vaccine is unsafe?

No, side effects are a sign of an immune system kicking into gear. They do not signal that the vaccine is unsafe.

How long will I be protected?

This will take time to fully determine across both the Pfizer and Moderna vaccines, as well as others in development. The process is going to involve periodic blood draws from volunteers to see what their antibody levels look like, though a decline in antibody levels doesn’t necessarily equate to loss of protection.

Do I need to wear a mask and avoid close contact with others after I am fully protected?

Yes. Not enough information is currently available to say if or when CDC will stop recommending that people wear masks and avoid close contact with others to help prevent the spread of the virus that causes COVID-19.

Can I get the vaccine if I’m pregnant?

Until findings are available from clinical trials and additional studies, only limited data is available on the safety of COVID-19 vaccines, including mRNA vaccines, administered during pregnancy. No safety concerns were demonstrated in rats that received the Moderna COVID-19 vaccine before or during pregnancy; studies of the Pfizer-BioNTech vaccine are ongoing. Both vaccine manufacturers are monitoring people in the clinical trials who became pregnant.

If individuals have questions about getting vaccinated, a discussion with a healthcare provider is recommended.

I am currently breastfeeding? Can I get the vaccine?

There is no data on the safety of COVID-19 vaccines in lactating women or on the effects of mRNA vaccines on the breastfed infant or on milk production/excretion. mRNA vaccines are not thought to be a risk to the breastfeeding infant.

If individuals have questions about getting vaccinated, a discussion with a healthcare provider is recommended.

Are there any other vaccines being made?

As of December 28, 2020, large-scale (Phase 3) clinical trials are in progress or being planned for three additional COVID-19 vaccines in the United States: AstraZeneca’s COVID-19 vaccine, Janssen’s COVID-19 vaccine, and Novavax’s COVID-19 vaccine​.

For more information on COVID-19 initiatives at Memorial Healthcare, visit For additional information from the CDC, please click here.


How can we help?

For compassionate care turn to Memorial Healthcare.
Give Us A Call!

Related Articles

Memorial Healthcare Recognized Among Best Hospitals for Maternity Care by U.S. News & World Report

Memorial Healthcare, an independent, community non-profit hospital in Shiawassee County, has been

Memorial Healthcare Board of Trustees Unanimously Adopts New System Model

New model allows for clearer delineation of business units, innovative service delivery

Memorial Healthcare Receives $4.7M Behavioral Health Services Grant

OWOSSO, Mich., November 8, 2023 – Memorial Healthcare, an independent, non-profit hospital

Memorial Healthcare Welcomes Congresswoman Elissa Slotkin

OWOSSO, Mich., September 18, 2023 – U.S. Congresswoman Elissa Slotkin visited the