On Monday evening, Dr. Stephen M. Hahn, director of the Food and Drug Administration, and Dr. Peter Marks, the director of the FDA's Center for Biologics Evaluation and Research (CBER), rejected a proposal from the U.S. government's Operation Warp Speed to dilute the current supply of coronavirus vaccines in order to boost supply.

During an interview on Sunday, Operation Warp Speed's chief, Dr. Moncef Slaoui, said his task force and Moderna (NASDAQ:MRNA) were in talks with the FDA about implementing the idea.

Physician in personal protective equipment with her hand up in a

Image source: Getty Images.

There may be signs of effectiveness at half the dosage tested in trials leading to Emergency Use Authorization of vaccines from Moderna and Pfizer (NYSE:PFE), but the companies didn't test those dosages specifically.  

Generally speaking, the immune responses seen in blood samples from people who receive half-sized dosages fall in line with immune responses produced by the authorized dose. While the FDA might be willing to use biomarker data to approve new seasonal flu vaccines, the virus responsible for COVID-19 isn't nearly as well understood. 

The FDA isn't going to authorize, or even condone, altered dosing of new COVID-19 vaccines without real-world outcome data. This includes suggestions that people injected once don't need to worry about coming back in a few weeks for their booster shot.

There were thousands of clinical trial participants who didn't show up for their booster shots, and they generally seem well protected. Since this wasn't a point that Pfizer or Moderna originally set out to prove, though, the FDA must insist that another clinical trial with the proposed dosing schedule be completed first.

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