Boston’s multifamily market is showing significant signs of stress, and it is leading the nation in an ominous metric that shows that stress could soon turn into distress.

More than 28% of Boston apartment properties with CMBS loans sit at less than 80% occupied, a new Trepp report shows, well above the national average of 4.8%. The vacancy, fueled by a flight to the suburbs and the lack of the city's typically large student population, has driven rents to drop precipitously in Boston.

The city with the next-highest percentage of multifamily properties below 80% occupancy was Santa Monica, California, at 22.8% while major East Coast metros Washington, D.C., and New York City recorded rates at approximately 7.5%, Trepp reported.

“This is not the ‘retail apocalypse’ or a step toward the 25% delinquency rate in the hotel space over the last year,” Trepp Senior Managing Director Manus Clancy wrote. “But savvy CMBS investors will keep an eye on this going forward for signs of distress.”

The coronavirus pandemic caused a flight to the suburbs as renters sought relief from Boston’s elevated apartment rents, which still top $2K for the average one-bedroom, even as the city's rents have declined 16% year-over-year.

Vacancy in Boston spiked to 9% last September around the city’s traditional moving period, according to Boston Pads, which tracks more than 182,000 apartments across Greater Boston. The city's vacancy has steadily declined to its current rate of 4.1%, which is more than 220% higher than it was a year earlier.