FDA Warns Against Tinkering With Pfizer, Moderna Vaccine Regimens After White House Advisor's Comments

The United States Food and Drug Administration warned against changing the dosing regimen, interval, or mixing of COVID-19 vaccines in a statement issued Monday.

What Happened: The health agency recognized that available data indicates the use of two specified doses of the COVID-19 vaccines — made by Pfizer Inc PFE and Moderna Inc MRNA — at specified intervals.

For the Pfizer vaccine, the interval is 21 days and for the Moderna vaccine, it is 28 days. 

FDA said using a single-dose regimen or administering less than the dose previously studied in the clinical trials without “understanding the nature of the depth and duration of protection that it provides is concerning.”

The regulator said that there is some indication that the depth of immune response is associated with the duration of the protection provided by the vaccines.

Why It Matters: The FDA acknowledged that there is a discussion about changing the dosing schedule or the doses so as to get more vaccines to the public quickly.

“Making such changes that are not supported by adequate scientific evidence may ultimately be counterproductive to public health,” said the FDA.

On Sunday, Operation Warp Speed Chief Adviser Moncef Slaoui had suggested that Moderna’s vaccine could be administered at half the regular volume to some people to further its availability. 

The head of the government’s vaccine effort had said that discussions were on with Moderna on using the reduced dosage. but the FDA would have the final say in the matter.

Price Action: Pfizer shares closed unchanged at $36.81 on Monday and fell 0.24% in the after-hours session. On the same day, Moderna shares closed 6.95% higher at $111.73 and gained 0.31% in the after-hours session.