Thread by @profshanecrotty

Why isn't there a Delta variant vaccine?

I hear this a lot. 🧵 Three reasons:
1. The regular vaccines give great booster responses against Delta and other variants.
2. “Original recipe’ vaccine is better suited for other variants
3. It is faster to proceed with original vaccines

1/ The regular vaccines give great booster responses against Delta and other variants
This was first shown by Moderna, with 'original recipe' vaccine booster, compare to Beta booster.
nature.com/articles/s4159…

And for T cells, the T cell epitopes between variants are highly conserved, so the 'original recipe' vaccine should be a good booster. Though no T cell booster data are published.
doi.org/10.1016/j.xcrm…

2/ The regular vaccine is better suited for other, non-Delta, variants
For example, the antigenic distance of original recipe is closer to both Delta and Beta than Delta is to Beta.
Summarized well by Derek Smith in his Pasteur Institute talk
covid19.conferences-pasteur.org/programme

There's a Science news article somewhere about this antigenic mapping….

3/ It is faster to proceed with 'original recipe' vaccines.
Speed matters, and regulatory approval and manufacturing is faster for the original vaccines.
(Manufacturing is faster because you don't have to split your resources.)