Florida Surgeon General's claim that updated COVID vaccines weren't clinically tested, including on humans, is misleading

The updated Moderna vaccine was tested in human trials and the Pfizer shot was tested in mice. Earlier versions of both vaccines have been tested in human trials.

On Sept. 11, the Food and Drug Administration (FDA) approved updated mRNA COVID-19 vaccines. These new vaccines target the XBB.1.5 sublineage of COVID-19, from which all of the currently circulating strains descend. A day later, the Centers for Disease Control and Prevention (CDC) issued a recommendation for all people 6 months and older to get the vaccine.

In a Sept. 13 roundtable, Florida Surgeon General Joseph Ladapo claimed that the recently approved vaccines lacked testing, and added that CDC advice that vaccination is still the best way to prevent hospitalization from severe illness isn’t backed by data.

“[CDC Director Mandy Cohen] made this statement without a drop of clinical trial data about these products that were just approved that say anything about their effectiveness or their safety in human beings,” Ladapo said. “And we are just at the point where you have the director of the CDC making very clear statements in the complete absence of data.”

Ladapo has had a history of vaccine skepticism. Last year, his Florida Department of Health recommended young men not take mRNA vaccines. And shortly before the approval of this year’s vaccines, he claimed that there has been “no clinical trial done in human beings” to support the vaccines’ approval.

VERIFY reader John emailed us to ask about the Florida Surgeon General’s claims. Another VERIFY reader asked if the latest COVID-19 vaccines were tested on humans before they were approved for use.


Were the 2023-2024 mRNA COVID vaccines approved without clinical trial data and human tests?



This is misleading.

Moderna tested its updated vaccine in a small clinical trial with human participants. Pfizer tested its updated vaccine in a trial using mice as subjects. These are almost identical to the mRNA COVID-19 vaccines that have been used and extensively tested over the last several years.


The FDA and the CDC based their approval of the updated mRNA COVID-19 vaccines on trials conducted by the manufacturers of the vaccines in combination with years of trial data on previous versions of the mRNA COVID-19 vaccines.

Moderna tested their updated vaccine with a clinical trial of a small set of human patients. Pfizer tested their updated vaccine with a preclinical study that used mice instead of people.

The data from Moderna’s trial indicated that the newest version of their vaccine is as safe as previous versions of the vaccine while better preparing immune systems to fight against currently circulating COVID-19 strains than those older versions of the vaccine. Pfizer’s data similarly indicated their newest vaccine better prepares immune systems for current COVID-19 strains.

Vaccines must go through rigorous testing that include human trials when they’re first developed, so scientists can gather data on the vaccine’s safety and effectiveness before they’re widely distributed and recommended to the public. This was the case for the original mRNA COVID-19 vaccines.

Updated versions of vaccines do not need to go through as much testing before they’re distributed to the public because they’re so similar to past versions of their vaccines that have already gone through those intense testing phases.

This is the case for both the updated Moderna and the Pfizer mRNA COVID-19 vaccines that have been updated and recommended for fighting COVID strains in fall 2023 and winter 2024.

"The flu vaccine is reformulated each year, based only on animal studies for the same reason," Yale infectious diseases physician Scott Roberts, M.D., told Yale Medicine last year when the omicron boosters were first approved. “We do an annual flu vaccine update based on the circulating strains of the flu, and unfortunately, we can’t wait on human data because we might not get that until November or December, well after many of us have been infected.” 

The ingredients in the newest versions of the Pfizer and Moderna vaccines are the same as the ingredients Pfizer and Moderna used in older versions of the vaccines.

The only differences between the new versions of these vaccines and their predecessors are that the new versions carry mRNA designed to look like a part of the XBB.1.5 strain, while the older versions carried mRNA designed to look like parts of previous strains of the COVID-19 virus.

RELATED: Yes, you can get the updated COVID vaccine for free. Here’s how

Even so, the manufacturers are continuing to test their vaccines.

Pfizer’s presentation of its vaccine data to the CDC included a slide that noted that a clinical trial for its updated vaccine is still ongoing, even though the company’s preclinical studies with mice demonstrated the vaccine to be effective. All previous versions of the vaccine have been studied for safety and effectiveness in their own preclinical and clinical trials, according to Pfizer’s slide.

Data from the National Library of Medicine’s Clinicaltrials.gov site shows that every version of the Moderna vaccine has had its own human clinical trial. A large clinical trial for the newest vaccine is still ongoing, and is expected to be completed in November 2023, according to clinicaltrials.gov.

The previous COVID-19 booster vaccines, which targeted the BA.4 and BA.5 subvariants of omicron, were similarly approved based on a mix of evidence from prior versions of the vaccines and data from preliminary testing of those vaccines.

 “The vaccines were authorized by regulators based on safety and effectiveness data from the original COVID-19 mRNA vaccines, as well as trials of the new formulation in mice,” Yale Medicine said of last year’s boosters. “Regulators also took into account data from human trials by Pfizer and Moderna of a similar reformulation, aimed at a previous version of Omicron, BA.1.”

Once the BA.4/BA.5 boosters were approved and released, the vaccine manufacturers were then able to collect more data based on the larger sample size of people taking the vaccines. Pfizer and Moderna both reported they found no new safety concerns in those vaccines a few months after the vaccines first became available to the public, Yale Medicine said.

Because COVID-19 vaccines have been taken by so many people around the world, there is a significant amount of data to suggest that the mRNA vaccines are effective in fighting COVID-19 and are safe for most people. 

RELATED: Yes, updated omicron boosters were tested on mice, not humans, before authorization

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