The worst case id your B12 may low but not detrimental.
So to take a B12 tablet is just a precaution but not an absolute.
The fact that most animals, including humans, are capable of storing long-term supplies of B12.
In humans, these stores may last for several years.
By the we both take it. Checked on quarterly blood work and is always above normal.
Now should we also worry about vitamin D
---
News flash: Most of the population (which eats TONS of meat and fish) is B12 deficient.
Please don't eat meat (and risk your health and that of the animals) for that reason. Just take the damn pill.