Three killed whole-cell oral vaccines are available for use in children and adults internationally but not in the US: A monovalent vaccine (travelers' diarrhea and cholera vaccine [Dukoral ®]) contains only V cholera O1 and El Tor bacteria plus a small amount of nontoxic b subunit cholera toxin; before taking, it must be mixed into buffer fluid (buffer packet is dissolved in 150 mL [5 oz] of cool water).