The omicron variant created substantial ridership and workforce headaches at the MBTA, but as the spread of new COVID-19 infections slows from an aggressive peak in early January, the public transit agency's outlook is improving.

Starting Monday, the commuter rail will return to a full service schedule, bringing back 26 trips per day that the T eliminated about three weeks earlier due to staffing shortages at commuter rail operator Keolis.

Most of those temporary cuts affected local service to Reading on the Haverhill Line and to Framingham on the Worcester Line.

The combination of a slower holiday season and the potent variant cut into already-depleted ridership across the MBTA network, MBTA General Manager Steve Poftak said Thursday, though he said there are signs the number of commuters has started to bounce back.

Ridership on the subway had been hovering around 50 percent of pre-COVID levels earlier in the winter but now stands around 40 percent, Poftak said. A recent "rising action" added about 30,000 riders per day, but the agency will need 60,000 to 70,000 more daily commuters to bring subway ridership back to where it was in late November, he said.

Bus ridership dropped from nearly 70 percent of the pre-pandemic baseline in November to just more than 40 percent amid the omicron surge and since then has rebounded back above 50 percent, while commuter rail fell from 50 percent to less than 30 percent.

"You see the trend that we've seen throughout the pandemic where bus ridership is the most durable overall, commuter rail is the most variable and subway falls somewhere in between," Poftak told the T's Board of Directors. "You're seeing that here, but I am encouraged by the fact that (commuter rail) ridership is already starting to rebound."