Deciphering the Data

mRNA vaccines have been well-tested

When the COVID-19 pandemic hit, previous work meant that mRNA vaccine candidates were ready fast. Next, a huge effort by scientists, doctors, and governments (plus hundreds of thousands of vaccine-taking volunteers!) made sure the final vaccines were tested both quickly and well.

By March of 2022, more than 210 million Americans had safely gotten their jabs. That's a lot of people!

To learn more about the foundational work that went into the mRNA vaccines, visit How mRNA Vaccines Were Engineered

mRNA vaccines save lives

Health officials continued collecting data on safety and efficacy, even after mRNA vaccines were widely available. This huge data set helped guide decisions—for health experts and individuals alike.

Looking to the data is especially helpful when individual outcomes—like who gets seriously ill from COVID—appear varied and unpredictable. You can learn about population level trends, or break down statistics by age, gender, and health status to get more personalized information. The analyses can help inform big picture policies that promote health and prevent disease. They can also help individuals understand what to expect from their decisions about vaccination.

The population-level graphs here show that the COVID-19 vaccines held up to real world use. Looking at the different outcomes for vaccinated versus unvaccinated people, the conclusion is clear. An mRNA vaccine could save your life.

Large data sets are powerful for detecting very rare events, too. In the fall and winter of 2021, the chance of a vaccinated person dying from COVID-19 was very low. For those with a booster shot, the death rate was near zero. This value is low enough that a small data set could miss it. But because there's so much data, it not only measures these rare deaths, it also sheds light on why they happened. That's an important step in prevention.

As everyone who experienced the COVID-19 pandemic knows, circumstances changed quickly. Infection levels fluctuated with the seasons, new variants surged, and vaccination rates increased. These graphs, too, tell the story of what happened as the pandemic changed over time. Tracking data this way can help us make sense of new situations that arise. For example, when new variants emerged after the vaccines were developed, many people wondered if their shots would hold up. And they did—the death rate for the vaccinated remained very low. Sadly, the difference between vaccinated and unvaccinated became even bigger when highly contagious forms of the virus were circulating.

Want to explore the data on your own? Click through the slides!

Vaccines make COVID-19 less dangerous than familiar risks

During the COVID-19 pandemic, people everywhere had to make decisions about their health amid changing risks. Yet one thing remained clear. As more data emerged, vaccine protection against serious disease held up, even for those most vulnerable to the virus.

Still, it can be difficult to see ourselves and our loved ones within the lines of a graph. It's even hard for experts who work with health data to predict the outcome for a specific individual. But there are ways to apply impersonal numbers to our everyday lives.

One is to see how a new threat (like a new virus) compares with familiar risks. The graphs show deaths from COVID-19 alongside deaths from other causes. Some—like cancer and the flu—have been among the top 10 causes of death in the US for many years.

The graphs show that for every 100,000 people in the US, nearly 8 unvaccinated people a week died from COVID-19. That's twice the number who died from cancer. But among people who were vaccinated and "boosted," deaths from COVID-19 were just 0.1 people per 100,000. That's one in a million—and much lower than the risk of death from accidental falls or car crashes.

Click through the slides to see more comparisons.

Vaccine complications are extremely rare

For an organization like the Food and Drug Administration (FDA) to approve a medication, it needs to be much safer than the illness that it treats. Vaccines are held to this standard too. And since healthy people take vaccines to prevent illness, the safety requirements are especially high.

That puts vaccines (including mRNA vaccines) among the safest medications we use.

They're so safe, any serious events that do happen are often reported as cases per million. That alone says a lot, since the total U.S. population was around 330 million in the 2020 census.

There are two serious events that have been reported following mRNA vaccines. They're referred to as “serious” because while they're certainly unpleasant, both events are treatable and only deadly in extremely rare circumstances.

  • Myocarditis, or inflammation of heart muscle, is estimated at 3-50 cases per million. (The range is because it's a little more common in young men compared to the general population.)
  • Anaphylaxis is a serious but treatable allergic reaction that's estimated at 5 cases per million.

But how rare is that, really? Flip over an unlikely event card to see how the numbers compare.

Viruses are much more dangerous than vaccines

Not only is the chance of a serious reaction from an mRNA vaccine extremely low, letting the virus run its course is a much bigger risk. Take myocarditis, for example. It's the most common serious event after having an mRNA vaccine. But, it's around 30 times more common in people with COVID-19. (The condition is still rare from either cause.)

Myocarditis is inflammation of the heart muscle, most often because the immune system has an extreme reaction to a viral or bacterial infection. Symptoms include chest pain, irregular heartbeat, and shortness of breath. For about 80% of “classic” cases (the ones not associated with COVID-19 or a vaccine), patients recover. Most vaccine-associated cases involved mild chest pain, and over 90% of patients make a full recovery with minimal or no medical treatment.

In contrast, myocarditis from COVID-19 tends to be more severe. The risk of long-term heart injury is around 100 times higher when COVID-19 is the cause, compared to vaccine-associated cases. It’s likely because COVID-19 puts additional stresses on a person’s heart.

Click through the slides to learn more.

It's normal to feel uncertain

When something is new, it's normal to feel confused or nervous. People differ in their tolerance to risk, and in the time it takes them to adjust to change.

Uncertainty is especially high when big questions remain unanswered. And there are some things we don't know yet about mRNA vaccines. Like how often we'll need boosters, or how well the vaccines will work against future variants of the virus.

Those unknowns, however, don't change what we do know. The vaccines are safe and effective against COVID-19. They save lives, and serious complications are incredibly rare compared to the unpredictable virus. During fast-moving public health challenges like the COVID-19 pandemic, vaccines are a powerful tool to protect ourselves and our communities.



Boehmer TK, Kompaniyets L, Lavery AM, et al. Association Between COVID-19 and Myocarditis Using Hospital-Based Administrative Data—United States, March 2020–January 2021. MMWR Morb Mortal Wkly Rep 2021;70:1228–1232.

Myocarditis and Pericarditis. Centers for Disease Control and Prevention. Accessed March 21, 2022.

Vaccine Safety Basics. World Health Organization. Accessed March 21, 2022.

Reported Adverse Events. Centers for Disease Control and Prevention. Accessed March 21, 2022.

Vaccine Adverse Event Reporting System (VARES). Centers for Disease Control and Prevention and Food and Drug Administration. Accessed February 22, 2022.

Heymans, S., & Cooper, L. T. (2021). Myocarditis after COVID-19 mRNA vaccination: clinical observations and potential mechanisms. Nature Reviews Cardiology, 1-3.

Heymans, S., Eriksson, U., Lehtonen, J., & Cooper, L. T. (2016). The quest for new approaches in myocarditis and inflammatory cardiomyopathy. Journal of the American College of Cardiology, 68(21), 2348-2364.

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Genetic Science Learning Center. (2022, May 12) Deciphering the Data. Retrieved December 01, 2023, from

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Genetic Science Learning Center. "Deciphering the Data." Learn.Genetics. May 12, 2022. Accessed December 1, 2023.