The requirement for B12 is very small, and it's easy to get through supplements (in the past, B12 was available by drinking water from streams and eating foods grown in soil, where the B12-making bacteria live--if the soil contains cobalt, and by B12 made in the mouth, but since we now drink chlorinated water, and our foods are thoroughly washed before we eat them---not to mention that the soil of conventionally-grown crops probably doesn't even contain cobalt---and we brush our teeth, we vegans have to make sure to get it somewhere else).
Don't panic, you probably have at least 2 years worth of B12 stored (no one knows how long it can be stored, but 2 years is the minimum I've seen, usually "at least 2-5 years worth," and some say up to 20 years, but that seems unlikely.
In addition to eating fortified food (yes, many cereals have B12 in, as do veggie 'milks' and nutritional yeast), you can get a B12 supplement. I like the methlycobalamin spray (
www.veganessentials.com carries a good one
https://secure1.nexternal.com/share...&Target=products.asp&Submit1.x=7&Submit1.y=13 ), which is a form of B12 that is more easily assimilated than the cyanabobalamin that one usually finds (the body has to break cyanocobalamin into methylcobalamin).
There are also sublingual methylcobalamin pills available. I used some to treat diabetic neuropathy in my now-departed cat Scooter, and he went from being unable to jump onto the sofa or walk downstairs to being almost 100% of normal after about a month of daily supplementation--and this was after the vet said that neuropathy is irreversible once one has it...that goodness for the internet!).
The less often you take B12, the less of it is absorbed, so if you take it less often, the total you take should be greater. For the spray, one spray 2-3 times a week would do fine. (But you probably get enough from the fortified foods you are already eating, or at least enough to take that down to a once-a-week spray 'just in case'.)
You definitely DON"T need a B12 shot. Most people suffering from B12 deficiency are NOT vegans, but have a problem with absorption--they lack something called 'intrinsic factor'-- that has nothing to do with their diet, hence, they have to take the vitamin in shot form.
Dr. Fuhrman has a multivitamin (Gentle Care) that is great for those of use following a plant-based diet. It contains B12 and other nutrients, but no vitamin A or beta carotene, which can be harmful in isolated supplement form).
As Carolyn says, I've been a vegan for about 15 years (the transition was not as clear cut as becoming a vegetarian over 30 years ago) and I'm not concerned about B12. The key is educating yourself. I read extensively, and I'm absolutely sure that this is the right path to be on.
One thing to watch out for. Seaweeds (like Nori and Dulse) contain a B12 analog that mimics B12 but does not have the same effects in the body. In fact, it can block uptake of actual B12. Those who rely on seaweeds for their B12 can end up with deficiencies. Some sources (especially some raw food advocates who shun supplements) claim that seaweeds are a good source of B12, which is a great disservice to their followers.
Some reading you might enjoy (to help put your mind at ease, as they all address the B12 issue):
"Becoming Vegan" by Brenda Davis and Vesanto Melina (a good overall source book)
"Prevent and Reverse Heart Disease" by Caldwell Esselstyn (promoting a low-fat vegan diet that he's used for over 20 years to reverse heart disease in his patients).
"Vegan Nutrition Pure and Simple" by Michael Klaper
"Food for Life" or "The Power of Your Plate" by Neal Barnard
(I've got a lot of other suggestions, if you're ever interested!)
(I didn't say that she was smart, just a co-worker!) She feels that if she consumes enough of it daily that some will at least get absorbed. Okay, so she's book smart, not common sense-smart!