Stand up for the facts!

Misinformation isn't going away just because it's a new year. Support trusted, factual information with a tax deductible contribution to PolitiFact.

More Info

I would like to contribute

In this March 29, 2021 file photo, a worker readies syringes with the Moderna COVID-19 vaccine in Metairie, La. (AP) In this March 29, 2021 file photo, a worker readies syringes with the Moderna COVID-19 vaccine in Metairie, La. (AP)

In this March 29, 2021 file photo, a worker readies syringes with the Moderna COVID-19 vaccine in Metairie, La. (AP)

Tom Kertscher
By Tom Kertscher June 25, 2021

mRNA COVID-19 vaccines were tested in humans, have proven to be safe, effective

If Your Time is short

  • The mRNA COVID-19 vaccines used in the U.S. (such as Moderna and Pfizer) were tested in humans, and have proven to be safe and effective.

A widely shared social media post claims that the technology used in two of the three COVID-19 vaccines used in the U.S. had not been tested in humans — and asserts that assurances it is safe and effective are wrong.

The post on Instagram, which also appeared on Twitter, states:

"mRNA technology has been around for decades. It had never gone past animal trials due to catastrophic side effects, including death. This technology was never 'fixed’. Now mankind is being pressured to take it, with assurances that it is safe and effective. That is bulls---."

The post was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.

The two vaccines that use mRNA technology, one made by Moderna and the other by Pfizer-BioNTech, were tested in tens of thousands of humans. They have been administered to more than 177 million people in the U.S. and have been shown to be safe and effective.

How the technology works

The messenger RNA, or mRNA, technology used to create the Moderna and Pfizer-BioNTech shots dates to the 1990s, though this is the first time it has been used in widely disseminated vaccines. 

These two mRNA vaccines use the human body’s natural immune response to their advantage. The shots give cells the directions for how to make a harmless  spike protein. Such spike proteins are found on the surface of the virus that causes COVID-19 — and it is these proteins that the virus uses to bind to cells. The immune system of a person who receives the mRNA vaccine then spots the unknown protein and makes antibodies to fight it. 

The third vaccine used in the U.S., by Johnson & Johnson, is different. Instead of RNA, it uses a disabled adenovirus to deliver instructions to produce the coronavirus’ spike proteins and activate the immune system. 

The testing

The mRNA technology previously was tested against other viruses like influenza; Moderna began its testing in 2015. In 2018, Pfizer and BioNTech announced a partnership to start developing an mRNA vaccine to prevent influenza. The various development efforts shifted to creating an mRNA vaccine for the coronavirus when the pandemic hit. 

Featured Fact-check

The testing of the COVID-19 mRNA vaccines was done on tens of thousands of people. Pfizer and Moderna got approval to test their shots on animals while simultaneously running Phase I trials on humans, prior to the vaccines getting emergency use authorization from the FDA in December 2020 for distribution to the general public. 

Safety and effectiveness

More than 177 million people have received at least one dose of a COVID-19 vaccine in the United States, with minimal complications reported despite the massive sample size.

Among people who are fully vaccinated, the mRNA vaccines reduce the risk of COVID-19, including severe illness, by 90% or more, according to the federal Centers for Disease Control and Prevention. 

While a number of claims have been made suggesting that the vaccine is unsafe or has resulted in dangerous side-effects, PolitiFact has found that most of them stem from incomplete use of data contained in a federal database known as Vaccine Adverse Event Reporting System, or VAERS. The database is a critical tool for researchers, but a breeding ground for misinformation about vaccine after-effects. Anyone can submit a report, and the reports are widely accessible. But the reports are not verified.

"Reports of adverse events to VAERS following vaccination, including deaths, do not necessarily mean that a vaccine caused a health problem," the CDC says. "A review of available clinical information, including death certificates, autopsy, and medical records, has not established a causal link to COVID-19 vaccines.". 

Serious adverse events after COVID-19 vaccination are rare but can occur. For example, CDC and FDA have confirmed 393 reports of myocarditis or pericarditis — inflammation of the heart — in people after mRNA vaccination.

Our ruling

A widely circulated social media post claimed that the mRNA technology in COVID-19 vaccines was never tested in humans, "now mankind is being pressured to take it, with assurances that it is safe and effective."

The two predominant COVID-19 vaccines in the U.S., Moderna and Pfizer, use mRNA technology and were tested in tens of thousands of humans before they were authorized. The clinical trials and the real-world results have shown both vaccines to be safe and effective. 

We rate the post False.

Our Sources

Instagram, post, June 21, 2021 

Lead Stories, "Fact Check: mRNA Vaccine Technology Does NOT Have Catastrophic Side Effects, Including Death," June 24, 2021

Health Feedback, "COVID-19 vaccines were tested in animals and clinical trials before receiving authorization; vaccinated people aren’t dying at a higher rate than unvaccinated people," May 18, 2021

PolitiFact, "Ask PolitiFact: How can COVID vaccines be safe when they were developed so fast?", March 29, 2021

PolitiFact, "Should I get a COVID-19 vaccination? Answering questions for vaccine skeptics," May 27, 2021

Centers for Disease Control and Prevention, "Pfizer-BioNTech COVID-19 Vaccine Overview and Safety," updated June 24, 2021

Centers for Disease Control and Prevention, "Moderna COVID-19 Vaccine Overview and Safety," updated June 11, 2021

Centers for Disease Control and Prevention, "COVID-19 vaccines work," updated May 20, 2021

Centers for Disease Control and Prevention, "Myocarditis and Pericarditis Following mRNA COVID-19 Vaccination," updated June 23, 2021

Centers for Disease Control and Prevention, "Safety of COVID-19 Vaccines," updated June 21, 2021

Centers for Disease Control and Prevention, "Selected Adverse Events Reported after COVID-19 Vaccination," updated June 23, 2021

New England Journal of Medicine, "Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine," Dec. 31, 2020

New England Journal of Medicine, "Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine," Feb. 4, 2021

Browse the Truth-O-Meter

More by Tom Kertscher

mRNA COVID-19 vaccines were tested in humans, have proven to be safe, effective

Support independent fact-checking.
Become a member!

In a world of wild talk and fake news, help us stand up for the facts.

Sign me up