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Why is there more than one type of COVID-19 vaccine?

Last Updated

April 12, 2021

The answers on this site were developed with and vetted by the CDC

Many teams of medical experts around the world have helped in the search for a safe and effective COVID-19 vaccine — including many of the leading doctors here in the United States.

Having multiple vaccines in development and production is crucial so that vaccination programs can be rolled out in many different countries at the same time, reaching as many people as possible.

Hundreds of millions of vaccine doses have already been distributed and hundreds of millions more are in production. New vaccine candidates are also in development which may provide more options, as well as additional quantities for the American people.

What is the viral vector vaccine?

Viral vector vaccines use a modified version of a different virus (the vector) to deliver important instructions to our cells. For COVID-19 viral vector vaccines, the vector (not the virus that causes COVID-19, but a different, harmless virus) will enter a cell in our body and then produce a harmless spike protein that is only found on the surface of the virus that causes COVID-19.

The cell displays the spike protein on its surface, which triggers our immune system to begin producing antibodies and activating other immune cells to fight off what it thinks is an infection.

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What types of vaccines are there?

Many vaccines work with harmless pieces of the spike-shaped proteins on the outer shell of the virus, instead of the entire virus. These proteins aren’t infectious — our immune system recognizes that the virus’ proteins in the vaccine don’t belong in our bodies and learns how to fight them off.

Both Messenger RNA (mRNA) and viral vector vaccines teach our bodies how to protect us from the viruses that contain them. They produce antibodies, which are part of our body’s immune system defenses, that fight off the virus if it enters our bodies. It’s important to note that none of these vaccines affect our DNA in any way.

How different vaccines work (CDC)
How well do they work?

So far, the data on the vaccines show that they are extremely effective at preventing severe illness from COVID-19. Clinical trials have been carried out on several COVID-19 vaccines to assess how effective they are. Other clinical trials are ongoing. The FDA has authorized some vaccines for use by the general public, after data from their trials showed them to be highly effective.

The vaccines will continue to be monitored closely in real-world conditions once they’ve been given to people, to ensure continued safety and to keep learning about things like whether you can still transmit the virus even if the vaccine protects you from being infected.

How well vaccines work (CDC)
Are mRNA vaccines safe?

Yes. mRNA vaccines have been in development for years and have been proven to be safe and effective. They build immune protection by copying the shape of the virus without actually including a piece of the virus itself.

mRNA stands for messenger ribonucleic acid and can most easily be described as instructions for how to make a protein, or even just a piece of a protein.

mRNA is not able to alter our genetic makeup (DNA). The mRNA from a COVID-19 vaccine does not affect or interact with our DNA in any way. Instead, COVID-19 vaccines that use mRNA work with the body’s natural defenses to safely develop immunity to disease.

More facts about vaccines (CDC)
What are the differences in the vaccines?

All authorized COVID-19 vaccines provide significant protection from serious illness and hospitalization. Getting vaccinated against COVID-19 and following CDC’s recommendations to protect yourself and others will offer the best protection from COVID-19.

There are currently 3 vaccines recommended by the FDA and CDC to protect against COVID-19.

The Moderna vaccine is recommended for people age 18+ and includes 2 shots spaced 28 days apart. It is a messenger RNA, or mRNA, vaccine. Based on evidence from clinical trials, the Moderna vaccine was 94% effective at preventing COVID-19 and provides significant protection against serious illness.

The Pfizer-BioNTech vaccine is recommended for people age 16+ and include 2 shots spaced 21 days apart. It is an mRNA vaccine. Based on evidence from clinical trials, the Pfizer-BioNTech vaccine was 95% effective at preventing COVID-19 and provides significant protection against serious illness.

The Johnson & Johnson/Janssen vaccine is recommended for people age 18+ and is delivered in one shot only. It is a viral vector vaccine. Based on evidence from clinical trials, the Johnson & Johnson vaccine was 72% effective at preventing COVID-19 and provides significant protection against serious illness.

Different COVID-19 vaccines (CDC)