Direct connection to Malpensa airport by high speed train Frecciarossa (to and from Naples, Rome, Florence and Bologna) is no longer on duty. According to Trenitalia the reason is to be found in the rail accident that happened in April 2012, over 600 km from Malpensa airport.
As a consequence of the rail wreck that put out of order two Frecciarossa trains, Trenitalia has had to reorganize the deployment of its available trains. Since the day of the accident in Roma Termini railway station, all Frecciarossa trains leave/arrive from/to Milano Centrale instead of heading to Malpensa airport Terminal 1 railway station.
In any case, it is possible to reach Malpensa airport from Milano Centrale by taking the Malpensa Express train leaving from platform 3.