Taken all together, the data suggest that at minimum, 20% of Americans still have had neither a vaccine, nor a prior infection. That’s about 66 million people who have immune systems that are completely “naive,” as scientists term it, when it comes to exposure to SARS-CoV-2.

Right now, the Centers for Disease Control estimates cases of omicron are doubling every two or three days in the U.S., and predict that in a few weeks, it could be the dominant variant across the country.

The 66 million Americans people who are naive to SARS-CoV-2 are the people for whom the omicron variant poses the greatest risk. These are the people who are most likely to end up in the hospital during an omicron surge. These are the people for whom a “less severe” variant in South Africa, may actually be a “severe” variant in the U.S.