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The Science Behind the COVID-19 Vaccines

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Posted by Glenn F. Rall, PhD

The COVID-19 vaccines were developed historically fast — less than 1 year from start to finish! This is an amazing scientific achievement and great news for everyone around the world. But the fast timeline has raised questions about whether the vaccines are safe and if they were tested long enough.

As a researcher who studies viral infections, I'll explain the science behind the vaccines and why they're safe and effective.

How are the first COVID-19 vaccines different from most other vaccines?

In the past, most vaccines used a weakened version of a live virus as a way of building immunity to that virus. The first 2 authorized COVID-19 vaccines are different. They use something called messenger RNA — or “mRNA” for short. mRNA is a tiny piece of genetic material that teaches cells in the body how to fight viruses. It has proven very effective.

Researchers have been studying mRNA for years. They have long thought it was a promising technology for vaccines, but this is the first time it’s being used in a vaccine that has received authorization from the U.S. Food and Drug Administration (FDA). This is a huge scientific breakthrough that may help us create other new vaccines in the future.

Learn more about the differences between the first COVID-19 vaccines >

How were these mRNA COVID vaccines developed so fast?

Vaccines historically take many years to develop, but that’s changing thanks to advances like using mRNA as the basis for the vaccine. This is good because the COVID-19 pandemic is a public health crisis that requires fast action. Developing a vaccine quickly was needed to prevent more people from dying. That’s why thousands of scientists worked around the clock to create these vaccines.

To speed up the COVID vaccine, many of the clinical trial phases overlapped with each other and downtime between research studies was eliminated to make the phases move faster. That does not mean the trials were unsafe or that any corners were cut. In fact, the trials were very safe and monitored closely.

Drug companies still had to prove to independent doctors and scientists not affiliated with the government or the companies that their vaccines were safe and effective before the FDA granted emergency use authorization (EUA). The only thing that was expedited was getting rid of a lot of the red tape that can hold up progress for many months.

All these things combined should help give you peace of mind that these vaccines are safe for you.

Get answers to common questions about getting the vaccine and what to expect >

Should I be worried about how fast these vaccines were developed?

No. Although the COVID-19 vaccines were developed quickly, they have gone through rigorous clinical trials with tens of thousands of people to make sure they’re safe and effective. This vaccine approach has been under development for over a decade.

The results of the clinical trials were also reviewed by independent scientists to validate the data. That’s why they were authorized for emergency use by the FDA. They would not have been authorized if there were doubts about their safety.

Has the vaccine been tested long enough to know whether there are any long-term side effects?

Long-term side effects are not expected. The FDA and the Centers for Disease Control and Protection (CDC) will continue to monitor the safety of the COVID vaccines far into the future to make sure they’re safe, and identify any possible long-term side effects.

If a safety issue is found, immediate action will take place to find out if the issue is related to the COVID-19 vaccine and determine the best course of action. It’s important to note, though, that while we do not have years of data on this vaccine, no one expects ANY long-term problems or side effects to occur.

Are there still unanswered questions about the vaccine?

Yes, there are questions the clinical trials have not yet answered. For example, we do not know how long immunity will last after you get the vaccine. There are other vaccines that require more than one shot over time. For example, the flu vaccine is needed every year and tetanus boosters are required every 10 years. This may be the case with the COVID-19 vaccine, but we do not know yet.

We also do not know yet whether people who get vaccinated can still pass on the virus to other people. That is being studied carefully now. Until we know more, you should still wear a mask even after getting vaccinated to protect the people around you. Getting answers to these questions will depend on more research in the coming months and years.

It’s understandable if you still feel uncertain about the right decision for you. But please know that these vaccines have been very thoroughly tested and are remarkably effective at preventing infection. And even more importantly — preventing the truly life-threatening consequences of COVID.

They’re safe, effective and the best way to end this pandemic. Thousands of doctors, scientists like me, nurses and public health officials support these vaccines, and we have received them ourselves.

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Glenn F. Rall, PhD

Dr. Rall is Professor and Chief Academic Officer at Fox Chase Cancer Center and co-author of Principles of Virology, 5th Edition. The focus of his work in the laboratory is to explore how the immune response functions in the central nervous system following viral infection.

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