I wanted to share one more figure from the #Omicron pre-print that I think offers some additional support for the idea that mRNA boosting doesn't just increase the total neutralizing response but instead "broadens" it to enable Omicron neuralization: 
What these graphs show is a comparison of neutralization activity against the original strain (wild type) on the X axis and either Delta or Omicron on the Y axis. White dots represent samples from recently vaccinated, black squares from recently boosted individuals.
If you look at the slope of the dashed line through the white dots, you'll see that it's quite flat (especially for Omicron). This means that after getting the primary series of shots, neutralizing activity against wild type doesn't really predict the activity against variants.
If you instead look at the slope of the solid line through the black dots, you'll see that it's much steeper. This means that after getting boosted, the neutralizing activity against wild type predicts the activity against variants, including Omicron!
The take-home message in these patterns is that the antibody response after boosting is fundamentally different than it was before. It's not just raising the level of the existing antibodies, it's doing a lot more than that. Calling the third shot a booster is oversimplifying!
Again, many thanks to @wilfredo_nk for generating all of the figures for the study and co-authors @kstdenis29 @EvanCLam @vivek_naranbhai and @MGHPathology for all of their efforts. Given the spread of Omicron we are seeing in genomic surveillance data, please #GetBoostedNow !
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