This key indicator may determine how bad a BA.2 wave could be in the US

With a new version of the Omicron coronavirus variant picking up steam in the United States, as many as 28 million seniors remain at risk of becoming severely ill from Covid-19, either because they are unvaccinated or partially vaccinated, or because it has been more than five months since their second or third dose of a vaccine, according to a CNN analysis of federal data.