An Overview of Pfizer's COVID-19 Vaccine

Pfizer's joint effort with BioNTech was the first vaccine approved in the U.S.

Pfizer’s BNT162b2 mRNA Covid-19 vaccine was the first vaccine against the novel coronavirus (COVID-19) approved for distribution in the United States. The approval came as an emergency use authorization on December 11, 2020, after clinical trials showed the vaccine was 95% effective in preventing COVID-19.

Pfizer vaccine
Getty Images

Pfizer and the German immunotherapy company BioNTech began working together on the COVID-19 vaccine in March 2020. The two companies began investigating mRNA vaccines together in 2018 to fight influenza. Clinical trials for the COVID-19 vaccine began in April 2020, and promising results from those trials led the companies to seek an emergency use authorization from the Food and Drug Administration (FDA) in November 2020.

When Was Pfizer's Vaccine Officially Approved?

The Pfizer-BioNTech COVID-19 vaccine received full FDA approval for individuals 16 and older on August 23, 2021, and for individuals 12 and older on July 08, 2022.

The vaccine, now marketed under the name Comirnaty, was the first COVID-19 vaccine to be granted FDA approval.

How It Works

The Pfizer-BioNTech vaccine is an mRNA vaccine, similar to the one developed by Moderna. The technology behind these vaccines has been around for about three decades and has shown promise in preventing notoriously difficult-to-prevent diseases like influenza and cancer. Unlike conventional vaccines that use inactivated or live viruses, mRNA vaccines contain no parts of the virus they fight.

An mRNA (messenger ribonucleic acid) vaccine uses a single-stranded molecule that complements a strand of your DNA. These strands have a special coating that can protect mRNA from chemicals in the body that can break it down, and help it enter cells.

Rather than exposing the body to a small amount of virus to create an immune response, mRNA causes the vaccine recipient to make the protein of interest. This includes:

  • Helping the cell make part of the spiked protein that makes COVID-19 so potent
  • Teaching immune cells to recognize and fight similar spiked proteins

According to the Centers for Disease Control and Prevention (CDC), mRNA vaccines teach our cells how to make a protein—or even just a piece of a protein. This triggers an immune response.

How Was Pfizer's Vaccine Tested?

The clinical trial investigated how well two 30-microgram doses given 21 days apart worked in preventing COVID-19. More than 40,000 people participated in the clinical trial between July and November 2020—half receiving the vaccine and the other half a placebo.

How Effective Is It?

The Pfizer vaccine has performed very well in clinical trials. The effective rate of the vaccine was 52% between the first and second dose of the vaccine, 91% a week after the second dose, and 95% effective beyond that. According to the clinical trial report, out of the 10 severe COVID-19 cases noted in the study population, only one had received the vaccine, and nine had received the placebo.

An additional clinical trial of 2,260 adolescents ages 12 to 15 found the vaccine to be 100% effective in these age groups and well tolerated.

Similarly, in a clinical trial for children ages 5 through 11 years, a lower dose of Pfizer's vaccine (10 micrograms) was shown to be 90.7% effective in preventing COVID-19.

In addition to the clinical trials, a CDC study of almost 4,000 healthcare personnel, first responders, and other frontline workers under real-world conditions found the mRNA vaccines (Pfizer and Moderna) to be 90% effective at least two weeks after the second dose.

The vaccine has also been shown to provide protection against emerging variants, including Omicron variants and the earlier Delta variants. A study published in The New England Journal of Medicine found one dose of the bivalent Pfizer booster to be 37% more effective against severe Omicron infection than one dose of the original booster.

How to Get It

The first Pfizer-BioNTech COVID-19 vaccine doses were given on December 14, 2020. As of April 2023, more than 400 million doses of the Pfizer vaccine have been administered in the U.S.

In addition, over 250 million doses of the Moderna vaccine have been administered and almost 19 million doses of the single-dose Johnson & Johnson vaccine have been given.

The CDC is leading vaccination efforts and all orders of the COVID-19 vaccines go through the agency.

COVID-19 vaccines are available in the U.S. Check your state health department and go to to find a site near you.

On February 25, 2021, the FDA announced that the Pfizer-BioNTech vaccine could be transported and stored at regular freezer temperatures for up to two weeks. This is in addition to spending five days in standard refrigeration temperatures immediately before administration. This update may help with distribution since it offers an alternative option to the vaccine's standard cold storage requirements of approximately minus 70 degrees Celsius.

All doses purchased by the U.S. government are free to its citizens. While the vaccine itself is free, the facility or agency that offers the vaccine may request reimbursement of administration fees from public health programs and insurance plans, but no one receiving a vaccine can be charged any fees or denied access if they don't have health insurance, according to the CDC.

Who Can Get the Pfizer-BioNTech Vaccine?

In April 2023, the FDA amended the EUAs for the Pfizer and Moderna mRNA vaccines, replacing the original, monovalent vaccines with the updated, bivalent vaccines. All doses of the Pfizer and Moderna vaccines, including the primary series, will now be bivalent doses.

Everyone 6 months and older can receive the Pfizer-BioNTech COVID-19 vaccine. In February 2023, the CDC added COVID-19 vaccination to its recommended immunization schedules for children, adolescents, and adults.

The original, monovalent vaccine was granted emergency use authorization (EUA) by the FDA for people aged 16 and up on December 11, 2020. It was later expanded to include adolescents ages 12 to 15 and children ages 6 months to 11 years. The EUA expansions followed results of clinical trials that found the vaccine to be effective and well tolerated for these age groups.

The vaccine was given full approval by the FDA on August 23, 2021, although it applied only for use in those 12 and older. The vaccine remained under EUA for children and adolescents 6 months to 11 years old.

On April 18, 2023, the FDA updated the EUA for Pfizer's updated, bivalent vaccine to allow it to be used for all vaccine doses, replacing the original vaccine. The original, monovalent vaccine is no longer authorized for use in the U.S.

How many doses of the Pfizer COVID-19 vaccine you need varies based on age. For most adults, you are considered up to date if you have received a bivalent dose, either as a booster or as your initial dose.

Children ages 6 months to 4 years can get up to three doses of the Pfizer bivalent vaccine, depending on how many doses of the original vaccine they received. For example, if a child received one dose of the original vaccine, their next two doses would be bivalent doses to complete the primary series.

The CDC and the American College of Obstetricians and Gynecologists each recommend that people who are pregnant get vaccinated. While safety monitoring is ongoing, studies have not found an increased risk for pregnancy complications from receiving an mRNA vaccine, according to the CDC.

Immunocompromised people have a higher risk of being hospitalized, becoming severely ill, or dying from COVID-19. The FDA has also authorized an additional dose of the vaccine for certain immunocompromised persons.

Who Is Eligible for the Pfizer-BioNTech Booster?

On September 21, 2021, the FDA first authorized the Pfizer vaccine to be given as a booster dose for certain populations. By the following May, everyone ages 5 years and older became eligible for a booster after finishing their primary series.

In August 2022, updated, bivalent boosters from Pfizer-BioNTech and Moderna received EUA from the FDA. These updated vaccines target both the original strain of the virus and the newer Omicron variants.

Bivalent vaccines have since replaced all previous monovalent vaccine doses, including primary doses. The CDC recommends that everyone ages 6 months and older get an updated bivalent dose.

Anyone who received a monovalent booster should receive a bivalent dose at least two months after the last monovalent booster dose. Some high-risk groups, including immunocompromised people and those ages 65 and older, may also receive additional boosters dose of a bivalent mRNA vaccine.

Side Effects and Adverse Events

Patients who were enrolled in the clinical trial were asked to keep a record of any local or systemic reactions after each dose of the vaccine. Mild to moderate pain at the site of injection was the most common complaint, with less than 1% of the trial group reporting severe pain. Most of the local reactions reported went away on their own in one to two days, according to the report.

Systemic effects—or reactions that affect the entire body—were more common in participants aged 16 to 55 than in participants who were older than 55. The most common effects were tiredness and headache. Less than 20% of the people who were vaccinated reported a fever after the second dose.

There were a few serious adverse reactions during the trial—one shoulder injury from the vaccination administration, inflammation of lymph nodes, cardiac arrhythmia, and limb pain or tingling. Two participants died—one from arterial disease and another from cardiac arrest, but researchers did not attribute either of these deaths to the vaccine itself. Another four people in the trial died, but they had received the placebo, not the vaccine.

Although it's rare, serious allergic reactions can occur after receiving the Pfizer vaccine. The Vaccine Adverse Event Reporting System (VAERS) reported that there were 21 cases of anaphylaxis, a life-threatening allergic reaction, after about 1.89 million first doses of the Pfizer-BioNTech vaccine (11.1 cases per million doses). Most cases occurred within 15 minutes of vaccination and no deaths were reported.

In a clinical trial that followed 3,100 individuals ages 5 to 11 who received the vaccine, the most commonly reported side effects were injection site pain, redness and swelling, fatigue, headache, muscle and/or joint pain, chills, fever, swollen lymph nodes, nausea, and decreased appetite. Overall, they were considered mild to moderate and usually went away within a day or two.

The most common side effects reported in clinical trials that followed children ages 6 months to 4 years were fever, irritability, decreased appetite, headache and pain, redness, and swelling at the injection site.

What Are Adverse Reactions?

Adverse reactions are considered to be medically significant adverse events caused by a vaccine, whereas a side effect is more common and mild reaction. Pfizer-BioNTech will continue safety monitoring for another two years on the initial trial group to watch for any additional reactions.

Risk of Myocarditis and Pericarditis

On June 25, 2021, the FDA announced an update to the Pfizer COVID-19 vaccine fact sheets for healthcare providers and vaccine recipients and caregivers about the rare risk of developing myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining outside the heart).

The CDC reported a rate of 12.6 cases per million second doses of Pfizer's or Moderna's vaccine within three weeks following vaccination among 12- to 39-year-olds. Cases have been predominately reported in male adolescents and young adults age 16 and older, with symptoms typically occurring within a few days after receiving the vaccine. Most people who developed these conditions have responded well to medication and rest.

The CDC continues to recommend the COVID-19 vaccine for those 12 years and older given the suggested increased risk of these conditions. However, the agency states that an eight-week interval between doses of the mRNA vaccine may be optimal for certain people to help reduce this risk.

Warning Symptoms

Seek immediate medical attention if you experience any of the following symptoms after vaccination:

  • Chest pain
  • Shortness of breath
  • Feelings of having a fast-beating, fluttering, or pounding heart

Funding and Development

Pfizer-BioNTech worked together on the vaccine with the help of an initial $1.95 billion in funding from the U.S. government as part of Operation Warp Speed and the Biomedical Advanced Research and Development Authority (BARDA)—a U.S. government program aimed at furthering the manufacture and distribution of vaccines to fight COVID-19.

According to Pfizer, the funds pay for the vaccine doses but were not used toward the research and development of the vaccine. The funding agreement entitled the U.S. government to the first 100 million vaccine doses the company produces, plus an option to purchase 500 million more doses after that. The government purchased an additional 200 million doses (100 million in December 2020 and 100 million in February 2021), bringing the total to 300 million doses ordered from Pfizer at a total cost of about $6 billion.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

25 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Polack FP, Thomas SJ, Kitchin N, et al. Safety and efficacy of the BNT162b2 mRNA COVID-19 vaccine. N Engl J Med. 2020;383(27):2603-2615. doi:10.1056/NEJMoa2034577

  2. Food and Drug Administration. FDA Approves First COVID-19 Vaccine.

  3. Pardi N, Hogan M, Porter, F, Weissman D. mRNA vaccines — a new era in vaccinology. Nat Rev Drug Discov. 2018;17(4):261-279. doi:10.1038/nrd.2017.243

  4. Centers for Disease Control and Prevention. Understanding mRNA COVID-19 vaccines.

  5. Pfizer. Pfizer-BioNTech announce positive topline results of pivotal COVID-19 vaccine study in adolescents.

  6. Food and Drug Administration. FDA authorizes Pfizer-BioNTech COVID-19 vaccine for emergency use in children 5 through 11 years of age.

  7. Thompson MG, Burgess JL, Naleway AL, et al. Interim estimates of vaccine effectiveness of BNT162b2 and mRNA-1273 COVID-19 vaccines in preventing SARS-CoV-2 infection among health care personnel, first responders, and other essential and frontline workers — eight U.S. Locations, December 2020–March 2021MMWR Morb Mortal Wkly Rep. 2021;70(13):495-500. doi:10.15585/mmwr.mm7013e3

  8. Lin DY, Xu Y, Gu Y, et al. Effectiveness of Bivalent Boosters against Severe Omicron InfectionN Engl J Med. 2023;388(8):764-766. doi:10.1056/NEJMc2215471

  9. Centers for Disease Control and Prevention. COVID-19 vaccinations in the United States.

  10. Food and Drug Administration. Coronavirus (COVID-19) update: FDA allows more flexible storage, transportation conditions for Pfizer-BioNTech COVID-19 vaccine.

  11. Centers for Disease Control and Prevention. Frequently asked questions about the COVID-19 vaccination.

  12. Food and Drug Administration. Coronavirus (COVID-19) Update: FDA Authorizes Changes to Simplify Use of Bivalent mRNA COVID-19 Vaccines.

  13. Pfizer. Pfizer and BioNTech announce positive topline results from pivotal trial of covid-19 vaccine in children 5 to 11 years.

  14. Food and Drug Administration. Pfizer-BioNTech COVID-19 Vaccines.

  15. Food and Drug Administration. Letter of Authorization.

  16. Centers for Disease Control and Prevention. Interim clinical considerations for use of COVID-19 vaccines currently approved or authorized in the United States.

  17. Food and Drug Administration. Coronavirus (COVID-19) Update: FDA Authorizes Bivalent Pfizer-BioNTech COVID-19 Vaccine as Booster Dose for Certain Children 6 Months through 4 Years of Age.

  18. Centers for Disease Control and Prevention. COVID-19 Vaccines While Pregnant or Breastfeeding.

  19. Centers for Disease Control and Prevention. COVID-19 Vaccines for Moderately to Severely Immunocompromised People.

  20. Centers for Disease Control and Prevention. Stay up to date with your COVID-19 vaccines.

  21. CDC COVID-19 Response Team, Food and Drug Administration. Allergic reactions including anaphylaxis after receipt of the first dose of Pfizer-BioNtech COVID-19 vaccine—United States, December 14–23, 2020MMWR Morb Mortal Wkly Rep. 2021;70(2);46-51. doi:10.15585/mmwr.mm7002e1

  22. Food and Drug Administration. Coronavirus (COVID-19) update: FDA authorizes Moderna and Pfizer-BioNTech COVID-19 vaccines for children down to 6 months of age.

  23. Food and Drug Administration. Coronavirus (COVID-19) update: June 25, 2021.

  24. Centers for Disease Control and Prevention. COVID-19 vaccine safety updates, Advisory Committee on Immunization Practices (ACIP).

  25. Department of Health & Human Services. Biden administration purchases additional doses of COVID-19 vaccines from Pfizer and Moderna.

By Rachael Zimlich, BSN, RN
Rachael is a freelance healthcare writer and critical care nurse based near Cleveland, Ohio.