I think it's really rare, and from what I read, it wasn't really a surprise to people who had that reaction. The ones I heard about it had epi pens. I figure if people have severe allergies, it might be predictable. Anaphylaxis is a response to an allergen - something that provokes an immune response. A vaccine provokes an immune response. Last I heard, they were advising people with severe allergies to avoid the shot. They have to have paramedics available at the vaccination sites.