An Overview of Pfizer's COVID-19 Vaccine

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

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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 Dec. 11 after clinical trials showed the vaccine was 95% effective in preventing COVID-19.

Pfizer vaccine

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Pfizer and the German immunotherapy company BioNTech began working together on the COVID-19 vaccine in March. 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 U.S. Food and Drug Administration (FDA) in November.

When Was Pfizer's Vaccine Officially Approved?

Pfizer's vaccine authorization was granted on Dec. 11. Almost immediately after, Pfizer began shipping doses of the vaccine.

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 is 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.

How To Get It

Pfizer/BioNTech were ready to start vaccinations just days after receiving a Dec. 11 emergency use authorization, with the first doses given Dec. 14. Initial supplies of the vaccination were tight, but as of Feb. 19, more than 30 million doses of the Pfizer vaccine were administered in the U.S. In addition, more than 29 million doses of the Moderna vaccine were administered.

The CDC is leading vaccination efforts, and all orders of the COVID-19 vaccine from Pfizer—or any other manufacturer—will go through the agency. CDC is overseeing the distribution of vaccines, too. CDC’s Advisory Committee on Immunization Practices (ACIP) has made recommendations on how to prioritize vaccine supplies. Healthcare workers and people living in long-term care facilities were the first to receive the first of the vaccines, which has been limited at first as manufacturing ramps up.

According to the CDC, there are more than 21 million healthcare providers in the U.S., and about 3 million Americans living in long-term care facilities. Each of these people would need to receive two doses of the mRNA vaccines, totaling nearly 50 million doses for these groups alone. The CDC estimates it will take several months before the supply of vaccines catches up to the demand. Guidance on who will receive the vaccine and when will be decided as supplies become available.

How Many Vaccine Doses Does America Need?

The U.S. alone has a population of about 330 million—meaning nearly 700 million vaccine doses will be needed to vaccinate all of America with two-dose vaccines.

Although little information is available yet on the specifics of when everyone will receive the vaccination, and where they can get it, state and local health departments will be coordinating efforts to distribute doses of the vaccines as they become available. The vaccine should be available both in physician offices and retail locations like pharmacies that administer other vaccines.

For now, the availability of the vaccine is somewhat limited due to its cold storage demands. The Pfizer/BioNTech vaccine has to be kept at around -70 degrees Celsius. A version of the vaccine that can be kept at standard refrigeration temperatures is expected to be developed later. The current formulation of the vaccine can be stored for five days in standard refrigeration temperatures immediately before administration.

Pfizer also announced on Feb. 19 that it submitted data to the FDA showing that the vaccine is stable at regular freezer temperatures for two weeks in addition to the five-days of standard refrigeration.

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 charge a fee for administration. Public health programs and insurance plans are expected to reimburse any costs associated with COVID-19 vaccination, and no one can be denied a vaccine if they are unable to pay a vaccine administration fee, according to the CDC.

Who Can Get the Pfizer/BioNTech Vaccine?

The Pfizer/BioNTech vaccine has been given emergency use authorization for people aged 16 and up. Safety information isn’t available yet or is too limited for children under age 16, pregnant women, and people who are immunocompromised. Additional data is expected in the coming months as additional trials are completed.

Pfizer announced on Feb 18 that a trial of the Pfizer vaccine in pregnant women, which will enroll about 4,000 people, began administering doses. The CDC says that individuals who are pregnant or immunocompromised can choose to get vaccinated when doses are available. 

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.

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.

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 and 100 million in February), bringing the total to 300 million doses ordered from Pfizer at a total cost of about $6 billion.

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