Why might our Omicron surge be different from the European one? Looking at the country as a whole, one big answer is obvious: Our vaccination rates are markedly lower than most European countries. (That is the hypothesis put forward by Burn-Murdoch, examining the divergent patterns of decoupling in the U.S. and U.K.) A second related answer is that we’ve done an even worse job, compared to our European peers, vaccinating and boosting the elderly. (Eric Topol of Scripps has emphasized this fact.) A third possibility is that the relatively high levels of severe disease we are seeing in New York and throughout the U.S. are the residue of that lingering Delta wave — either the effect of some limited amount of ongoing spread of the more virulent variant or the impact of cases that began their clinical cycle a few weeks ago and are still requiring treatment in the hospital. In some parts of Europe, like France, Omicron has been growing on top of Delta, but most of the continent and the U.K. had not been dealing with nearly as much severe disease this fall as the U.S. has been. This is Gounder’s hypothesis, echoed by other doctors and public-health officials who are advising caution in making any assessment of the American wave before Omicron truly takes over the hospitals — that we should wait for another week or two of data to see a clear picture of the new variant unclouded by the old one…

But one apparent difference between New York and Europe may also prove significant, if our Omicron wave continues to be more severe: Even though our vaccination rates may be comparable, we appear to be seeing a much bigger share of cases among the unvaccinated here than they have over there.