Here's the link to the MMWR report:
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5204a1.htm
edited to add the following quote from the link posted above:
Persons who follow vegetarian diets should ensure adequate cobalamin intake. The only reliable unfortified sources are animal products, including meat, dairy products, and eggs. Most naturally
occurring plant sources of cobalamin are not bioavailable; however, plant foods fortified with cobalamin, such as some cereals, meat analogs, soy or rice beverages, and nutritional yeast (7), can be
reliable and regular sources. The content of fortified food is usually listed on the food label and ingredient list. Fortified food and supplements made from cobalamin (e.g., cyanocobalamin) provide
cobalamin that is physiologically active in humans (6). Products whose labels do not specify cobalamin and list only vitamin B12 might include nonbioavailable sources. Vegetarians, particularly women
during pregnancy and lactation, should be knowledgeable about the cobalamin content of their food or seek nutritional advice. Few of the common infant-toddler cereals are fortified with cobalamin (8).
Breast milk from mothers with adequate nutritional status, infant formula, cow's milk, or a cobalamin-fortified soy or rice beverage provide a cobalamin source for infants and children. If it is not possible
to acquire the recommended dietary intake of cobalamin through food, a daily supplement should be taken that contains at least the recommended dietary intake of cobalamin from a reliable source.a