Collateral damage is from people who missed things like chemo treatments (which for some bizarre reason were deemed "elective"), cancer screenings, A1c tests, and other preventative care that finds treatable but potentially fatal conditions. On average 5k Americans per day are diagnosed with cancer. On average 2k Americans per day die from some form of cardiovascular disease. That adds up in a hurry when treatment and preventative care for those conditions are limited to the point they have been over the last couple months.
The effects of lockdowns and social distancing is a whole other debate which I don't have the energy to get into (and probably belongs on the poli board anyway).