Short answer: most probably, not.
Long answer:
A sudden transition from a vegetarian diet to a omnivorous one will clearly have some effects, as any sudden change in diet will have. According to this article, these problems may appear:
A person might have a little problem if he or she started right out on a huge steak. Their body might not have sufficient levels of the right enzymes. Along the same lines, it can be hard to digest any large meal after a long fast or period of starvation.
However, there is a little (< 1%) chance of having meat allergy:
A very few – less than one percent of the population – are allergic to meats from common livestock, such as pork and beef. If a vegetarian has this kind of allergy, she could have a reaction from just a speck of these meats.