This post was published by Jon Fleetwood. Support him by subscribing at Substack and following at Instagram / X / Facebook.
The U.S. Food and Drug Administration approved Moderna’s new XFG-formulated COVID-19 vaccines on August 27, 81 days before a human study specifically designed to evaluate the safety and immune response of the new formulations was scheduled to begin.
Pfizer’s XFG COVID vaccine formulation was approved on the same day, equally without safety data for its new formulation.
FDA approved the 2026–2027 formulas for Moderna’s SPIKEVAX and mNEXSPIKE vaccines, which are claimed to contain genetic instructions corresponding to the alleged JN.1-lineage XFG subvariant.
But FDA’s own Aug 27 approval letters show that a Phase 3b/4 human study specifically evaluating the “Immunogenicity and Safety of MNEXSPIKE and SPIKEVAX 2026-2027 Formula” is not scheduled to begin until November 16.
The first interim results are not due until March 26, 2027.
For younger children eligible to receive the new SPIKEVAX formulation, a separate human safety and immunogenicity study is scheduled to begin even later.
In other words, FDA approved Moderna’s new XFG vaccines first.
The human studies specifically evaluating the new formulations come afterward.
The regulatory pathway allows FDA to rely on claimed evidence from previously licensed formulations rather than require a new human safety trial of every updated formulation before approval.
But that raises consequential health, informed-consent, regulatory, and accountability questions:
- How can FDA determine that a newly reformulated vaccine is safe before formulation-specific human safety data exist?
- What evidence justifies carrying earlier safety findings forward to a changed product?
- And why is FDA requiring a Phase 3b/4 study specifically to evaluate the new formulas’ “Safety” only after Americans are permitted to receive them?
- And most fundamentally, if FDA is approving a newly reformulated vaccine before human safety data specific to that formulation exist, is the agency fulfilling its responsibility to independently establish that products are safe before Americans receive them, or shifting that uncertainty onto the public and collecting the answers afterward?
Congressional committees have confirmed that the FDA “is not meeting important federal safety requirements to protect its employees and the public while also failing to prioritize scientific data quality delivered from FDA laboratories.”
You can contact the FDA here.
And Moderna here.
FDA Approved the XFG Formula August 27
FDA’s Aug 27 approval letter for SPIKEVAX states: “We have approved your request received June 5, 2026, to supplement your Biologics License Application (BLA) … to include the 2026-2027 Formula and associated labeling revisions.”
The agency issued a corresponding approval for the 2026–2027 formula of mNEXSPIKE the same day.
SPIKEVAX is now approved for everyone 65 and older, as well as people ages 6 months through 64 years with at least one underlying condition FDA claims puts them at high risk for severe COVID-19.
mNEXSPIKE is approved for everyone 65 and older and qualifying people ages 12 through 64.
FDA’s prescribing information identifies SPIKEVAX specifically as the “2026-2027 Formula.”
But the approval letters reveal that the prospective human study evaluating the safety and immune response of that formula had not yet begun.
Human Safety Study Starts 81 Days Later
FDA lists the following postmarketing commitment for both Moderna vaccines: “A Phase 3b/4 Randomized, Open-label Study to Evaluate Immunogenicity and Safety of MNEXSPIKE and SPIKEVAX 2026-2027 Formula”
The study will examine people 65 and older and people ages 12 through 64 with risk factors for what the agency calls severe COVID-19.
FDA gives the following schedule:
- FDA approval: Aug 27, 2026
- Study initiation: Nov 16, 2026
- Study completion: Jan 15, 2027
- Interim results: March 26, 2027
- Final report: June 15, 2027
That means 81 days separate FDA approval from the scheduled beginning of the human study specifically evaluating the safety and immunogenicity of Moderna’s new XFG formulations.
And the company does not have to wait for those results.
Moderna said following the approval that its updated vaccines were expected to become available “in the coming days.”
Children’s Study Starts Even Later
FDA’s SPIKEVAX approval letter identifies another Phase 3b/4 study specifically evaluating the 2026–2027 formulation in children.
The agency describes it as a study: “to Evaluate the Safety and Immunogenicity of SPIKEVAX 2026-2027 Formula”
The study covers children ages 6 months through 11 years with qualifying risk factors.
It is scheduled to begin Dec 31, 2026.
That is 126 days after FDA approved the formulation.
Yet FDA’s newly approved prescribing information allows SPIKEVAX to be administered to qualifying children beginning at 6 months old.
So for that population, FDA approval precedes the scheduled XFG-specific human study by more than four months.
How Can FDA Get Away With This?
Congress did not pass a law specifically allowing FDA to approve updated vaccines without first obtaining human safety data from the new formulation.
FDA itself created the legally binding framework in 21 CFR § 601.12 under authority delegated by Congress, allowing changes to already licensed biologics to be supported by “clinical and/or nonclinical laboratory studies.”
This raises questions about why the agency responsible for protecting Americans from unsafe products permits newly changed vaccines to reach people before their formulation-specific human safety studies even begin.
Bottom Line
FDA approved Moderna’s new XFG COVID-19 vaccines 81 days before the human study specifically designed to evaluate the new formulas’ alleged safety and immune response was scheduled to begin.
And 126 days before the corresponding study in younger children.
This was not because Congress specifically exempted updated vaccines from new human safety testing.
FDA itself created the regulatory framework that allows changes to licensed biologics to be supported by “clinical and/or nonclinical laboratory studies,” permitting the agency to approve a changed formulation without first obtaining human safety data specific to that formulation.
That puts responsibility for the decision squarely on FDA: The agency charged with determining that biologics are safe approved Moderna’s changed vaccines before the human studies specifically evaluating the safety of those changes had even begun.
Americans are therefore being permitted to receive the new formulations while the very human safety evidence FDA has required for those formulations is still scheduled to be collected afterward.
If FDA can approve a changed vaccine before obtaining human safety data on the change itself, what exactly does an FDA determination of “safe” guarantee to the Americans expected to rely on it?
FDA approved Moderna’s new XFG COVID-19 vaccines 81 days before the human study specifically designed to evaluate the new formulas’ alleged safety and immune response was scheduled to begin.
And 126 days before the corresponding study in younger children.
This was not because Congress specifically exempted updated vaccines from new human safety testing.
FDA itself created the regulatory framework that allows changes to licensed biologics to be supported by “clinical and/or nonclinical laboratory studies,” permitting the agency to approve a changed formulation without first obtaining human safety data specific to that formulation.
That puts responsibility for the decision squarely on FDA: The agency charged with determining that biologics are safe approved Moderna’s changed vaccines before the human studies specifically evaluating the safety of those changes had even begun.
Americans are therefore being permitted to receive the new formulations while the very human safety evidence FDA has required for those formulations is still scheduled to be collected afterward.
If FDA can approve a changed vaccine before obtaining human safety data on the change itself, what exactly does an FDA determination of “safe” guarantee to the Americans expected to rely on it?
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