* 100,000 children out of reach in rebel-held Raqqa province
* Some 2.15 million Syrian children vaccinated against polio
* Red Cross says food, medicines run short in besieged areas
By Stephanie Nebehay
GENEVA, Jan 13 (Reuters) - Heavy fighting has prevented health workers from getting polio vaccine to an estimated 100,000 Syrian children in the northeastern province of Raqqa, United ...