Definition of "trivalent" [triv•a•lent]

• Having valence 3. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "A review of 31 studies published over four decades found that the most widely used seasonal flu vaccine, known as trivalent inactivated vaccine, was only 59 per cent effective in healthy adults."
• "It will be decided later whether vaccine-makers put them all in one shot, a so-called trivalent dose, or split them up."
• "According to the Health Protection Agency, the vast majority of those who died had not had this season's "trivalent" vaccine, which protects against three strains of flu."