The Omicron BA.2 subvariant now accounts for most cases in the country, with the number of BA.2.12.1 subvariant cases on the rise particularly in the Northeast.

But even those numbers don’t offer a full picture of the virus’ presence in the country, CDC officials said on Tuesday. A soon-to-be-released CDC study indicates that from December to February there were an estimated three infections per reported case, varying by region, Kristie Clarke, co-lead for the agency’s COVID-19 Epidemiology and Surveillance Taskforce Seroprevalence Team, said during a briefing with reporters.

The rise in the presence of antibodies from 43 percent of Americans in January to 57 percent in February was also faster than CDC officials expected.

Clarke cautioned that the fact that most Americans now have antibodies does not guarantee them protection from reinfection or any kind of group immunity, noting that there is still not a known threshold at which the virus stops circulating.

In children in particular, Covid-19 can be severe, with 20 to 30 percent of children hospitalized with the virus going into intensive care units, and children developing post-Covid conditions, Clarke noted.

“As a pediatrician and a parent, I would absolutely continue to endorse that children get vaccinated, even if they have been previously infected,” she said.

Vaccination rates among children in particular remain very low, with only 35 percent of children aged 5 to 11 having received at least one dose, and vaccinations still unavailable for children under five.