With all the reports of people turning down Moderna for their 2nd shot, looks like it's time for a 🧵comparing the two mRNA vaccines: Moderna & Pfizer.
Here's the composition of the two vaccines. Worth noting that they use the identical mRNA template for the spike protein with a modification of the uracil nucleoside residues that have been shown to increase the level of neutralizing antibodies elicited. 
Now let's look at the pre-VOC clinical trial vaccine efficacy(VE) side by side. Pfizer on the left, Moderna on the right below. Both had virtually identical VE: 94.8% vs, 94.1%
With some data on the clinical efficacy of Moderna against Beta & Delta still pending, they appear equivalent when looking at neutralizing antibody titres elicited in Phase 2 trials of Moderna.
Here's an indirect comparison of Pfizer & Moderna from a study of U.S. HCWs again showing equal VE in a real-world population with perhaps an edge going to Moderna.
What about vaccine safety? Here's some great graphics from an article in @HealthyDebate comparing adverse effects amongst vaccines approved in Canada including Pfizer & Moderna.
With all this showing that the 2 mRNA vaccines are virtually the same, why do so many people want Pfizer over Moderna?
The answer may be due to availability bias, an increased tendency to favour recently acquired information because of its ease of recall, a form of "branding".
The answer may be due to availability bias, an increased tendency to favour recently acquired information because of its ease of recall, a form of "branding".
Bottom line: Even though we have a paucity of data on having 2 different mRNA vaccines for a 1st & 2nd shot, the likelihood that there would be a clinically meaningful difference in VE & safety is very small. Think of the 2 vaccines as good buddies both of whom are helpful./End
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