Type 1 hypersensitivity reactions to anti-viral vaccines are relatively common amongst domestic animals such as dogs, cats and ferrets. The question that these reactions then raise is: what type of immunological profile do these animals display on subsequent protection to one (or more) of the viruses that they were vaccinated for? This question is the basis of a project I am involved in with Dr. Susana Mendez who studies vaccinations at the Baker Institute. There is good reason to investigate the question posed above: hypersensitivity reactions are mediated by IgE and IgG1 (in the dog) antibody production and are commonly associated with a T-helper (Th2) environment. This is a classic response to extracellular pathogens such as parasitic worms; in this case, the development of a Th2 response results in expulsion of the parasite and protection of the host. Conversely, exacerbated Th2 responses are responsible for pathological conditions such as asthma or allergy. However, viruses are intracellular pathogens, and intracellular immunity is achieved through the elicitation of a Th1 immune response. The objective of this study is to determine whether the hypersensitivity reaction may alter the anti-viral protective Th1 response that is intended to be achieved by vaccination.