Ruch-Gallie RA, Veir JK, Hawley JR et al: Results of molecular diagnostic assays targeting feline herpesvirus-1 and feline calicivirus in adult cats administered modified live vaccines, J Feline Med Surg 13:541, 2011.
Diagnostic testing to identify the cause of a respiratory infection in a cat today often involves molecular testing of swabs collected from the nasal and pharyngeal areas. These assays detect the genetic material of the virus of interest. These molecular assays, known as real-time polymerase chain reaction (RT-PCR), are very sensitive, able to detect very small amounts virus. Vaccines given to cats, including cats entering shelters, are usually live virus vaccines. When respiratory disease occurs in these cats soon after vaccination, the concern is that the molecular assays may detect the vaccine virus, confusing the diagnosis. These researchers investigated the likelihood of detecting virus in the days immediately following vaccination. They tested multiple samples collected from six cats given an intranasal vaccine and six given a subcutaneous vaccine. Overall, the detection of virus within days after vaccination was uncommon. The risk was slightly higher with intranasal vaccines versus the subcutaneous vaccines. But the percentage of samples collected that gave positive results was quite small. Thus, the risk of false positive results from vaccination appears to be low. [MK]
Maggs D, Clarke H: Relative sensitivity of polymerase chain reaction assays used for detection of feline herpesvirus type 1 DNA in clinical samples and commercial vaccines, Am J Vet Res 66:1550, 2005.