From the European Medicine Agency: Feline endogenous retrovirus RD114 in some live attenuated vaccines commercially available in the EU for use in animals 15 September 2010 http://www.vmd.defra.gov.uk/pdf/vaccines_CVMPassessmentRD114.pdf "Under natural conditions, retrovirus RD114 is not known to cause diseases, whatever the species (including human beings). However, injection through vaccines of retrovirus RD114 live replicative particles, even at very low level, does not mimic natural conditions of contact between retrovirus RD114 and animals or humans. The consequences of inoculating replicative retrovirus RD114 to animals or humans are not foreseeable." "In general, canine and human cell lines are more sensitive than feline cell fines to retrovirus RD114 infection in vitro. All these points taken together, the risk that retrovirus RD114 can integrate into the genome of humans, dogs or big felidae, although theoretical at this stage, cannot be ruled out." "Due to self-injections of cat or dogs vaccines, humans may be exposed, but to a much lesser extent as self injections occur only on an ad hoc basis and as it is very likely that a full dose will not be injected. Moreover, human beings are likely to have been exposed for a prolonged period to retrovirus RD114 through the long-standing domestication of cats, potentially with systemic exposure to replicative virus in the case of scratches and bites."