Yes, CARRIERS is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, R 1, R 1, I 1, E 1, R 1, S 1.

Is it a valid word?

CARRIERS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

someone whose employment involves carrying something
a self-propelled wheeled vehicle designed specifically to carry something
a large warship that carries planes and has a long flat deck for takeoffs and landings
an inactive substance that is a vehicle for a radioactive tracer of the same substance and that assists in its recovery after some chemical reaction
a person or firm in the business of transporting people or goods or messages
a radio wave that can be modulated in order to transmit a signal
a man who delivers the mail
a boy who delivers newspapers
(medicine) a person (or animal) who has some pathogen to which he is immune but who can pass it on to others
a rack attached to a vehicle; for carrying luggage or skis or the like
(genetics) an organism that possesses a recessive gene whose effect is masked by a dominant allele; the associated trait is not apparent but can be passed on to offspring

Also: aircraft carrier, attack aircraft carrier, common carrier, carrier wave, mail carrier, letter carrier, immune carrier.