This past week brought a very significant pandemic-related development in the emergence and rapid spread of XEC, the newest recombinant Omicron variant.
Normal viral reproduction essentially produces huge numbers of clone virus particles, with occasional mutations which, as they accumulate over a period of months, can eventually produce new and more infectious variants. Recombination is a near-instantaneous pathway to generating novel variants. It occurs in the rare instances when a human cell happens to be simultaneously infected by two particles of different strains. Both hijack that cell’s gene-copying mechanism as usual, but the resulting viral particles are essentially random assortments of the parental genes. If, when the resulting reshuffled particles kill the cell and spread through the infected person’s body, one happens to have a combination of genes which is more effective at evading their victim’s existing immunity, natural selection will ensure that the new strain is more likely to be spread when that person infects others.
As illustrated by the CDC bar chart in our composite chart for this week, KP3.1.1 outcompeted all of its cousin strains over the past several months, quickly spreading to become the dominant variant based on having the highest-yet Omicron infectivity. XEC’s 20-fold rise from only 0.3% of new US COVID infections to 6.0% in less than two months suggests that it is even more adept than KP3.1.1 in evading the human immune system and could rapidly achieve dominance in this winter’s respiratory virus season.
The latest Public Health Canada data shows XEC to be spreading at least as quickly here in Canada.
The good news in the above is that XEC appears to be a recombination of KS.1.1 and KP3.3, both of which are in the same JN family against which the newly-approved seasonal booster shot was formulated and don’t appear to result in more severe symptoms. That approval is fortunate given that existing immunity is rapidly waning in all of us who have had neither a booster nor were infected in the past six months. I’m anxiously awaiting my local pharmacy’s receipt of the new vaccine, which I’m told will be within the next few weeks. In the meantime, I’ll be wearing my N95 at the supermarket and in all other crowded indoor spaces.