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

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 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. 

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. 

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.

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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.

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.