FDA Warns Against Half-Dosing Pfizer, Moderna COVID-19 Vaccines

January 06, 2021 - FDA is warning health officials to follow the authorized dosing schedules for COVID-19 vaccines as the first round of recipients become eligible to receive their second dose. 

Despite discussions about half-dosing vaccines approved for emergency use, extending the length of time between doses, or mixing and matching doses to immunize more people against the coronavirus, the agency stated that any change to the schedule is “premature and not rooted solidly in the available evidence.”

“Without appropriate data supporting such changes in vaccine administration, we run a significant risk of placing public health at risk, undermining the historic vaccination efforts to protect the population from COVID-19,” FDA stated. 

“The available data continue to support the use of two specified doses of each authorized vaccine at specified intervals,” they continued.

Since the beginning of the pandemic, pharmaceutical companies have been racing to develop a COVID-19 vaccine. Now, two vaccine candidates – one from Pfizer and the other from Moderna – are pulling ahead.

Both vaccine candidates have been approved for emergency use authorization by the FDA after demonstrating over 90 percent efficacy in clinical trials.

The vaccines also both require two doses to achieve the elevated level of efficacy according to clinical trial results. The dosing interval for the Pfizer vaccine known as BNT162b2 is 21 days between the first and second doses, while the interval for Moderna’s mRNA-1273 vaccine is 28 days.

Giving a major group of Americans a half dose of the respective vaccines will accelerate the rollout and speed up immunizations against COVID-19.

But FDA and other major figures, including NIAID Director Anthony Fauci, MD, believe that this strategy may go against the science and wouldn’t fix the pressing issues facing the US rollout.

Specifically, FDA stressed that the first dose of each respective vaccine candidate is commonly being misinterpreted. 

In the Phase 3 trials, 98 percent of participants in the Pfizer-BioNTech trial and 92 percent of participants in the Moderna trial received two doses of the vaccine at either a three or four- week interval, respectively.

But those individuals who did not receive two vaccine doses at either interval week were only followed for a short period-of-time, FDA stated. Therefore, the agency cannot conclude anything about the duration of protection after a single-dose of a vaccine from the single-dose percentages reported by each company. 

“Using a single dose regimen and/or administering less than the dose studied in the clinical trials without understanding the nature of the depth and duration of protection that it provides is concerning, as there is some indication that the depth of the immune response is associated with the duration of protection provided,” FDA said. 

“If people do not truly know how protective a vaccine is, there is the potential for harm because they may assume that they are fully protected when they are not, and accordingly, alter their behavior to take unnecessary risks,” the agency continued. 

Ultimately, any changes to the dosing schedule for any COVID-19 vaccine are not supported by scientific evidence and may be counterproductive to public health. 

Therefore, until vaccine manufacturers have data and science supporting change, FDA “strongly recommends” that healthcare providers follow the FDA-authorized dosing schedule for each vaccine candidate. 
As of the beginning of this week, nearly 15.4 million doses of the respective vaccines have been distributed throughout the US, according to the CDC. The leading states include Maine, Vermont, Connecticut, Tennessee, Montana, and Alaska.