sets on several routes will be less frequent between Tuesday and January 28, with the changes mainly affecting the central belt, with some sets from Edinburgh and Glasgow also impacted.
ScotRail says the reduced timetable will provide customers with greater certainty.
Passengers have been asked to check the position of their journey before they head to the stop.
Alex Hynes, managing director of ScotRail, told the BBC’s Good Morning Scotland radio programme on Tuesday that the reductions affected around 160 of the 2,000 sets the company typically runs each day.
Covid Scotland: ScotRail running substitute buses after raft of cancellations, …
Mr Hynes said: “We’ve got hundreds of staff across the business absent due to Covid.
“Where that affects drivers and conductors, clearly that results in cancellations.
“So, we’ve decided to proactively introduce a new timetable from today to function slightly fewer sets.”
Mr Hynes said he did not believe there was a higher rate of virus transmission among rail staff than the general population.
He continued: “We’ve seen record case numbers yesterday, 20,000 in Scotland.
“The complete population is being affected by that – our crews are part of that population.”
Asked if the reductions may have to last longer than expected, he said: “One thing we’ve learned with Covid is it’s very difficult to forecast what will happen next and I speculate there will be a few twists and turns in the Covid story before it’s over.
“What we’re saying is that we’re going to function the current timetable for the period of January, but clearly we keep this under literally daily review.”
Click: See details