**Short answer:** most likely 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][1], 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 (indipendent of the fact one is Vegetarian or not):

> 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.


  [1]: http://sciencenordic.com/does-meat-make-vegetarians-ill