For veterinary professionals
November 1, 2026
When the Medgene RHDV2 vaccine first reached practices, it came in one presentation: a 10-dose vial labeled for immediate use [1]. If you saw rabbits then, you remember what that meant. We built vaccine clinics around the vial, filled appointments in groups of ten, and hoped nobody canceled.
I wanted to know whether an opened vial, handled carefully and kept refrigerated, would stay free of bacterial and fungal growth long enough to make individual appointments realistic. With my coauthors, and with cultures run by the Bacteriology/Mycology laboratory at the University of Tennessee College of Veterinary Medicine, that question became a short paper in the Journal of Exotic Pet Medicine [1]. Single-dose vials have since changed the picture, and I'll get to that. The data and their limits are still worth walking through.
The vaccine is a killed recombinant subunit product targeting the VP60 protein of RHDV2 [1]. It contains two preservatives, gentamicin and thimerosal, which is why we considered it an excellent candidate for extended use [1]. Both preservatives appear, alone or together, in other multidose products, including the European RHDV2 vaccine Eravac and the IMRAB 3 rabies vaccine [1].
The label pushed many practices toward scheduled vaccine clinics, with all the logistics that come with them [1]. We modeled the design on a study of liposomal bupivacaine, a preservative-free single-use vial that stayed sterile for several days when used in a multiple-dose manner [1, 11].
Three vials of the Medgene RHDV2 vaccine were stored at 5°C on a refrigerator shelf, and the metal caps were removed from all vials at the start [1]. One person collected every sample at the same time each day. Before each draw, the vial was gently inverted 10 times, wiped with an alcohol pad and allowed to air dry. Each 0.5 mL sample was drawn with a sterile 25 gauge needle on a 1 mL syringe [1].
The first two vials were punctured daily, 0.5 mL at a time, until 10 samples had been collected from each. The third vial served as the control and was punctured on the last day of the study [1]. Collections ran Monday through Thursday so samples reached the lab promptly, and the study spanned 16 days [1].
After each draw, the needle was changed and the sample was injected into a sterile no-additive tube through an alcohol-swabbed stopper. Samples were shipped overnight on an ice pack to the bacteriology diagnostic laboratory [1]. Aerobic bacterial culture was run on samples from collection days 1 through 10, for 21 cultures, and fungal culture on samples from days 5 and 10, for 5 cultures [1]:
We calculated 95% confidence intervals using the Newcombe method with a continuity correction [1].
Nothing grew. None of the samples showed aerobic bacterial growth (0/21, 95% CI 0 to 0.19) or fungal growth (0/5, 95% CI 0 to 0.54) [1].
Those upper bounds deserve as much attention as the zeros. Twenty-one negative cultures still leave room for a true contamination rate as high as 19 percent, and five fungal cultures leave room for 54 percent. Zero growth in a small sample is encouraging. It is not proof.
The preservatives, together with aseptic technique, likely account for what we saw [1]. Our conclusion was that, with appropriate aseptic precautions, the vaccine "could potentially be used extra-label, once fully approved by the USDA, as a multidose vial for at least 16 calendar days without compromising sterility, pending pyrogen and endotoxin testing as well as anaerobic cultures and potentially next generation DNA sequencing" [1].
In the paper we said the vaccine remained "at least partially sterile" for 16 days [1]. I still think that is the right level of confidence.
The USDA Center for Veterinary Biologics granted Medgene's vaccine emergency use authorization in 2021 and a conditional license in November 2023 [8]. APHIS lists it as product 474-1R00R0, Rabbit Hemorrhagic Disease Vaccine, Serotype 2, Killed Baculovirus Vector [7]. Medgene's March 2025 announcement still described the rabbit license as conditional [9].
The same announcement introduced single-dose vials, sold in 20-count clamshells [9]. At Priest Lake Veterinary Hospital we now use single-dose vials. For most practices, that solves the scheduling problem that led to this study. The data still apply to anyone working from a multidose vial, and they are a reminder of how much handling matters.
My reading: protection against death is strong, individual antibody responses vary and fade over a year, and that supports keeping every rabbit on an annual booster.
The paper names what a definitive answer would take: repeated studies with more vials and more controls, pyrogen and endotoxin testing, anaerobic and special media cultures, possibly next generation DNA sequencing, and testing beyond 16 days to match how long some clinics keep a bottle in use [1]. Until that work exists, I treat 16 days of careful aseptic use as the outer edge of what our data support.
This study was self-funded. I have no financial relationship with Medgene.
If you want to talk through vaccine handling, a rabbit with sudden illness, or the RHDV2 vaccine schedule for a tricky patient, I'm glad to hear from you. You can read the family version of this topic in Be a Hare-O: Protect Your Rabbit From RHDV2 and our earlier post on RHDV2 vaccination in Tennessee. See the referral information for veterinarians, or call Priest Lake Veterinary Hospital at (615) 361-4646.
This content is for educational purposes for veterinary professionals. It doesn't establish a VCPR or replace clinical judgment for an individual patient. Drug use and doses should be checked against current references and adjusted for each case.