Without more data from China and further intelligence reports from governments, both zoonotic and lab-leak origin hypotheses remain on the table.
As global proportions rapidly grow, an initial assessment suggests a low public health risk.
Partial immunity from COVID in residents early in the pandemic and infection-prevention measures may explain the findings, the authors say.
Hospitalized patients more often had 3 or more impaired cognitive domains than non-hospitalized participants did.
Though levels are still very low, early indicators show regional rises.
Hawaii this week warned about increasing cases, with test positivity now at 12.4%.
The mRNA COVID vaccine used this past season showed no elevated risk of any of the 29 serious adverse events assessed.
Effectiveness was 70% to 85% against hospitalization for the 2 mRNA vaccines.
The CDC said COVID-19 activity is rising in several parts of the country and test positivity and emergency department visits are up nationally.
