The above chart shows positive PCR tests per age group per week in the Canton of Zurich in Switzerland. The picture is similar in most of Europe: the increase in positive test results since late summer is mostly due to people of school and working age (20 to 40 and 40 to 60), not senior citizens and the elderly. Therefore, hospitalizations and deaths have remained low.
Moreover, according to antibody data, the first infection wave was at least ten times bigger than shown in the above PCR test diagram. To understand the full magnitude of this discrepancy between virus transmission speed and testing capacity, consider this impressive chart by the Economist.