G.R. Holyoak at Oklahoma State University did some work on this several years ago, but for the life of me I cannot find a publication of the results...
If my memory serves me correctly, there is a concern about transmission of the virus, primarily because embryos are usually flushed at ~7 days post ovulation and along with the embryo there will be other matter flushed from the uterus of the donor mare and this may include virus which can attach to the fertilized oocyte (aka "embryo" even though it's not technically correct). Although the "embryos" are washed prior to transfer, I think the findings were that not all virus were removed.
To be on the safe side, if you can't find Dr. Holyoak's research either (and if you do, please post the results or a link to them here!!) it would be best to either vaccinate the recipient mare or contact Dr. Holyoak at OSU to get the answer (and if you do that, please let us know that reply too!!).
Please note that opinions, product information, advice or suggestions posted on this bulletin board are not necessarily those of the management at Equine-Reproduction.com nor does the maintenance of the post position indicate an implicit or any endorsement of that information, opinion or product.
Further, although we have the greatest respect for the posters offering assistance here, you are advised to seek a consultation with your veterinarian prior to using information obtained from this board if it is of a veterinary nature.Proud to be sponsored and supported by: