NEW YORK — The number of U.S. suicides fell nearly 6% last year amid the coronavirus pandemic — the largest annual decline in at least four decades, according to preliminary government data.

Death certificates are still coming in and the count could rise. But officials expect a substantial decline will endure, despite worries that COVID-19 could lead to more suicides.

It is hard to say exactly why suicide deaths dropped so much, but one factor may be a phenomenon seen in the early stages of wars and national disasters, some experts suggested.

“There’s a heroism phase in every disaster period, where we’re banding together and expressing lots of messages of support that we’re in this together,” said Dr. Christine Moutier, chief medical officer of the American Foundation for Suicide Prevention.