Former Vice President Joseph R. Biden Jr. won Alaska’s Democratic primary on Saturday night, the first nominating contest held since Senator Bernie Sanders dropped out of the race and made Mr. Biden the party’s presumptive presidential nominee.

With all precincts reporting, Mr. Biden won 55 percent of the vote and Mr. Sanders won 45 percent.

The state’s primary, which awards 15 pledged delegates, was turned into mail-in voting after concerns of the global coronavirus pandemic scrapped plans for in-person voting sites. Alaska had originally scheduled its primary for April 4, before the pandemic, but was among 16 states and Puerto Rico that postponed their voting because of the outbreak.

Mr. Biden’s hold on the Democratic nomination, long likely since his romp on Super Tuesday, became all but official once Mr. Sanders left the race on Wednesday. Though several candidates still appeared on Alaska’s ballot, just as they would in other states, the former vice president is expected to cruise through the remaining primaries without complication.

Alaska uses a ranked choice voting system. According to The Associated Press, the state Democratic Party received about 19,000 mail-in ballots, an increase in participation over the 2016 cycle — when the state used a caucus system. It continues a trend seen in several states this year, which has seen participation increase as they have switched from a caucus system to primaries.