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3 Pfizer-BioNTech COVID vaccine bottles with needle syringe

Three vaccines, developed by pharmaceutical companies Pfizer-BioNTech, Moderna and Johnson & Johnson have received emergency use authorization by the FDA. Both the Pfizer-BioNtech and Moderna vaccines are showing about 95 percent efficacy in their preliminary reviews. This means people who received these vaccines in clinical trials had a 95 percent lower risk of getting COVID-19 than people in the trial’s control group who did not receive a vaccine. The Johnson & Johnson vaccine showed 72 percent efficacy in U.S. clinical trials.

All three vaccines were 100 percent effective at preventing hospitalizations and deaths from COVID-19 during the clinical trials. More types of vaccines are expected to be authorized for use and given out in the coming months.

Types of COVID Vaccines Available or in Development

There are three main types of COVID vaccines that are currently available in the United States or are part of large-scale (Phase 3) clinical trials. COVID-19 vaccines can help recipients develop immunity to the virus. They may help prevent you from becoming seriously ill or dying if you are infected with COVID-19 or from getting the virus at all. It is impossible for any of these types of COVID vaccines to cause you to become infected with COVID-19 or to change your DNA.

The three types of COVID vaccines are:

  • Messenger RNA (mRNA) vaccine
  • Protein subunit vaccine
  • Vector vaccine

How Messenger RNA (mRNA) Vaccines Work


The Pfizer-BioNtech and Moderna vaccines both are mRNA vaccines, which work differently than many other types of vaccines. mRNA vaccines train your immune system to make antibodies for specific diseases without injecting the virus into your body.

Typically, vaccines work by injecting a tiny part of a virus called an antigen into your body. This type of vaccine is called a live attenuated vaccine. The amount injected is not enough to make you sick, but it makes your immune system create cells called antibodies that can fight that particular antigen. Then, if your body experiences the antigen again, it will remember it and quickly produce more antibodies to defend itself.

Instead, mRNA vaccines use messenger RNA, a piece of genetic code that tells our cells what to do, like make new proteins or repair damage. mRNA is naturally found in all of our cells, but in 2005, infectious disease experts at Penn Medicine discovered how to modify mRNA to safely make our cells create proteins similar to those found in some viruses. Once those proteins are made, our immune systems can then create antibodies for that virus.

Today, this same technology is being used by scientists around the world and here at Penn Medicine to develop vaccines for not only coronaviruses but all kinds of diseases, including genital herpes, influenza, and HIV.

How Protein Subunit Vaccines Work

Protein subunit vaccines work by injecting only small pieces of the COVID-19 virus that best stimulate your immune system, rather than the whole germ.

These COVID vaccines include spike proteins (S proteins) that your immune system recognizes as not belonging in your body. It then creates antibodies, so your body remembers the virus and can fight COVID-19 if you become infected in the future.

Novavax is currently developing a protein subunit vaccine for COVID-19, which entered a large-scale clinical trial on Dec. 28, 2020.

How Vector Vaccines Work

The Johnson & Johnson vaccine is a vector vaccine. Vector vaccines use genetic material from the COVID-19 virus that is placed inside a weakened version of another virus, such as the virus that causes the common cold.

The weakened virus is then injected into your body, delivering information from the COVID virus. That information instructs your cells to copy the spike protein that is unique to COVID-19 and create antibodies against the virus

AstraZeneca and the University of Oxford in England are also developing a viral vector COVID-19 vaccine. The Oxford-AstaZeneca vaccine entered a large-scale clinical trial in August 2020 that was paused in early September and resumed on Oct. 23, 2020, in the United States.