Niantic has announced that Pokémon GO will be running a holiday event from December 25th to January 3rd. During this event, PokéStops will award a one-use Incubator everyday after your first spin. Johto Eggs and Festive Pikachus have also gained higher encounter rates as well.
Lastly, from December 30th to January 8th, encounters for the Kanto starters and their evolutions will be raised highly. Lure Modules will also be raised from 30 minutes to 60 minutes, giving you an even higher chance of catching Bulbasaur, Squirtle, Charmander, and each of their evolutions.