As you are doubtless aware, the FDA scientific advisory board today voted to recommend approval of Moderna’s Covid-19 vaccine under Emergency Use Authorization, and it is expected that the FDA will grant this on Friday, adding tens of millions of potential vaccine doses to our supply.
What is the difference between the two now-approved vaccines? While there is no peer-reviewed publication for Moderna’s entry as there was for Pfizer’s, the FDA did release the 54- page application the company provided, which I have reviewed. Spoiler alert! Not much.
The Moderna and Pfizer vaccines use almost identical technology: RNA coding for the “spike protein,” in lipid nanoparticles to allow entry into body cells. Both conducted large Phase 3 trials; Pfizer’s was slightly larger, about 18,800 people in each arm of the trial compared to 13,900. Both showed roughly 95% efficacy in preventing symptomatic Covid-19. Both also showed reduction in severe cases, with the edge here perhaps to Moderna. In the Pfizer study, after the first dose, there were 9 severe cases in placebo recipients and 1 in the vaccine group. In the Moderna study, the numbers were 11 and zero.
Side effects were similar in both studies, and I will not repeat these.
One possible advantage to Pfizer was that efficacy seemed similar across all age groups, while the Moderna study showed lower efficacy in subjects over 65: 95.6% in those 18-64, 86.4% in those 65 or older.
An obvious advantage to Moderna is that its vaccine can be stored at less demanding conditions: it should be stored at -13 to 5 degrees F, while Pfizer’s needs temperatures of -70C (-94F). Buy dry ice!!
How about Bell’s palsy, which was in the news? In the Moderna study, there were four cases of this condition, in which there is paralysis on one side of the face, usually (but not always) temporary, 3 in the vaccine group and 1 in the placebo group. To put this in perspective, Bell’s palsy is a common condition. With 30,000 people followed for 2-3 months, you would expect 2-3 cases, so while this needs to be watched for, it is not a major concern.
Bottom line: very similar, and either seems both effective and safe.
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