The Covid-19 pandemic has boosted retirements among baby boomers, further straining the tight labor supply and leaving a hole for employers to fill.

Older workers who could least afford to retire early—those with lower incomes and less education—have been more likely to leave the workforce during the pandemic, researchers have found. The question is whether their retreat is temporary or permanent. Some retired because of Covid-19 fears, and others after failing to find suitable work.

The rising value of stocks, homes and other assets also has prompted a group of more affluent boomers to also retire earlier than expected, economists said. Other researchers believe the rise in the number of retirees is because fewer of them are re-entering the workforce.

The shifting labor force is complicating the work of economic policy makers trying to determine which jobs lost in the pandemic will return and how many American workers will be available to fill them. So far, it isn’t clear if recent retirees will be lured back to work by better jobs and pay—or because they miss their working lives—and how many are gone for good.