Antigenic similarity between the dominant variants.

Here is how antigenically similar the currently circulating variants XEC and KP.3.1.1 are to KP.2 (what the Moderna and Pfizer vaccines target).

1 antigenic unit (AU) is relatively minor.

For context, the original wild type coronavirus is about ~7 AUs different than these variants.

Our first vaccine update to BA.5 was about ~4 AUs different than the original wild type coronavirus.

The second vaccine update to XBB.1.5 was about ~2 AUs different than BA.5.

And the current vaccine update to KP.2 was about ~6 AUs different than XBB.1.5.

The CDC and FDA are generally looking at annual vaccine strain updates like the flu vaccine (though there was some debate on that).

But for now the current vaccines do protect against XEC and KP.3.1.1. They are still relatively close to those variants.