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Two half or full shots of Moderna COVID vaccine yield similar antibody levels: Data Byte

Jan 6, 2021 | 1:30 AM GMT

Immunogenicity data from Moderna’s COVID-19 vaccine hint that prime-boost vaccination with half the authorized dose may provide the same level of protection as the full dose.

The data lend at least some weight to the idea of stretching supplies by administering two 50 μg shots instead of two 100 μg shots. The catch, however, is that correlates of protection have not yet been established for COVID-19 vaccines, which means decision-makers are still largely groping in the dark.

In Phase IIa testing, mean neutralizing antibody levels evoked by Moderna COVID-19 Vaccine (mRNA-1273) were nearly identical after two injections of either 50 or 100 µg of the mRNA vaccine. The doses also produced comparable responses in the company’s Phase I trial.

Both studies found that prior to the booster shot, mean titers in subjects who had received a single injection of the half dose were slightly lower than those in subjects given the authorized dose, and had overlapping confidence intervals. 

In the Phase IIa study, the gap between the 50 μg and 100 μg doses closed after the second injection.

Operation Warp Speed Chief Scientific Adviser Moncef Slaoui has touted the idea of providing two 50 μg shots of Moderna COVID-19 Vaccine to make supplies go further, based on the immune responses in the trials.

In a statement issued Jan. 4, FDA rebuffed proposals to alter vaccination dosages or schedules for either Moderna COVID-19 Vaccine or Comirnaty (BNT162b2) from Pfizer Inc. (NYSE:PFE) and BioNTech SE (NASDAQ:BNTX).

In the statement, FDA Commissioner Stephen Hahn and Peter Marks, director of the Center for Biologics Evaluation and Research (CBER), cited potential for harm because individuals “may assume that they are fully protected when they are not, and, accordingly, alter their behavior to take unnecessary risks.”

Hahn and Marks also said  FDA would “continue to strongly recommend” that healthcare providers adhere to the authorized regimens until vaccine manufacturers “have data and science supporting a change.”

In a Dec. 23 statement Slaoui made to reporters, he said NIH is in active discussions with Moderna about testing a lower dose, but did not provide a timetable for the trials.

In theory, Moderna could get a hint of the 50 µg dose’s efficacy by amending its Phase IIa study, which remains ongoing, to collect data on COVID-19 cases, although the number of confirmed COVID cases expected in the placebo group of a 600-subject study would be low. The pivotal COVE trial enrolled over 30,000 subjects and had 185 confirmed cases at a Nov. 21 cutoff date.

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