There is a possibility of copycat attacks. Jewish organizations are advised to increase their level of vigilance. From WNBC News:

The NYPD is putting extra patrols and security in place in Jewish communities and synagogues Wednesday, after a deadly explosion on a bus in Bulgaria carrying Israeli tourists, department spokesman Paul Browne said.

Four people were killed and at least 30 injured in the explosion at an airport in Burgas, which Bulgarian officials did not confirm as terror-related but which the Israeli prime minister blamed on Iran.

The stepped-up security in New York is precautionary, Browne said.