Domestic vaccine for lethal rabbit virus available

USDA grants emergency-use authorization as virus spreads

October 15, 2021 (published)
Photo courtesy of Dawn Sailer
This weekend, Lemuel (above) and 10 other rabbits owned by Dawn Sailer of Indianapolis are scheduled to receive a vaccine that protects against a virulent and often fatal rabbit disease. The domestically produced vaccine became available after the federal government in September granted emergency-use authorization.

Dawn Sailer has big plans this weekend. She will be taking 11 long-haired rescue rabbits to her veterinarian in Indianapolis. After more than a year of hearing about the unchecked spread across North America of a highly contagious, lethal rabbit virus, Sailer will begin immunizing her furry crew — because for the first time, she can.

Last month, the U.S. Department of Agriculture Center for Veterinary Biologics granted emergency-use authorization for an experimental vaccine produced by Medgene Labs, a biotechnology company in Brookings, South Dakota. Since then, the vaccine has been cleared for distribution by animal health officials in 32 states, including Indiana. Until now, the only way to combat rabbit hemorrhagic disease virus type 2 in Sailer's state – and most others — has been with rigorous biosecurity protocols that veterinarians admit can be hard for the average rabbit owner to follow. 

"There was this kind of feeling of dread," said Sailer, who, as the president of the board for House Rabbit Society, a national rabbit rescue and education organization, knew the virulent virus was coming her way. "Now, it's so exciting to be able to be proactive and protect our rabbits.”

Easily spread and highly resilient, the virus responsible for rabbit hemorrhagic disease causes lesions throughout internal organs and tissues, particularly the liver, lungs and heart, resulting in bleeding. It is often fatal. There are many strains of RHDV and three major viral subtypes: RHDV (or "classical RHDV"), RHDVa and RHDV2 (sometimes called RHDVb). Treatment is generally limited to supportive care, with infected rabbits kept in isolation. The virus does not infect humans.

Classified as a foreign animal disease, RHDV2 surfaced in the U.S. in 2018 and 2019 in a few isolated cases affecting domestic rabbits. When it was confirmed to be in wild cottontails and jackrabbits in several Southwest states in March and April 2020, officials and veterinarians who monitor the virus predicted it would eventually become endemic in North America.

To date, the current RHDV2 outbreak has been identified in 16 states, mostly in the West and Southwest, according to Mike Stepien, a USDA Animal and Plant Health Inspection Service spokesperson. (The House Rabbit Society keeps a running list on its website.) It also has been confirmed in many states in Mexico and one Canadian province. 

Since 2020, veterinarians, mainly in states with verified occurrences, have been permitted to use two vaccines imported from Europe, where RHDV2 has been endemic for years. The process for importing Eravac (from Hipra in Spain) and Filavac (from Filavie in France) varies by state and is complicated, costly and time-consuming. 

In brief

Now veterinarians in states that have approved distribution, documentation and reporting requirements for the Medgene vaccine can order it directly from the company. Additional states are working through the approval process, and Medgene regularly updates the list of states on its website. Any adverse reactions must be reported to Medgene Labs, which is required to report them to the USDA-CVB. 

The company said it had shipped 5,500 doses to 13 states as of Thursday.

Company's first foray into rabbit medicine

Founded in 2011, Medgene has mainly focused on developing vaccines for cows, pigs and deer, and conducting disease surveillance for veterinarians and food producers. The RHDV2 vaccine is the first that is likely to have widespread use in pets. The company began working on a vaccine shortly after learning of the first verified cases in wild rabbits in the U.S.

Unlike the European vaccines, only Medgene's has been tested using the virus circulating in the United States, according to the USDA's Stepien.

Medgene CEO Mark Luecke called the emergency-use authorization "a milestone" for state veterinarians and rabbit owners.

"Many people across the U.S. have been dealing with this devastating disease without an adequate solution," he said in a statement provided to the VIN News Service. "We are working diligently to formalize the reporting requirements within every state with the goal of helping rabbit owners gain access to the vaccine as quickly as possible."

Medgene has completed an efficacy study, a very brief summary of which is posted on the company's RHDV2 webpage. The company is in the process of completing the safety studies required to qualify for a conditional license from the USDA, which is an intermediate step toward full licensure. 

Medgene, Eravac and Filavac vaccines are all administered as subcutaneous injections and provide reported protection rates of 90% or better.

Medgene's vaccine design, however, is different from that of Eravac and Filavac. The latter two products use inactivated virus derived from the livers of rabbits infected in a lab. Medgene uses recombinant technology, similar to the Pfizer-BioNTech and Moderna COVID-19 vaccines.

But unlike the COVID-19 vaccines, which deliver genetic material that prompts the body to build a viral protein that stimulates an immune response, Medgene's vaccine delivers the immunogenic protein directly to the body.

Eravac and Filavac require one shot, with immunity built in seven days and lasting for 12 months. Medgene's current recommended protocol is an initial two-dose regimen with the second dose 21 days after the first (with immunity built 14 days after the second dose), followed by a single-dose annual booster.

"Additional studies are planned to further our understanding of the duration of immunity and revaccination protocol," Jason Melby, a spokesperson for the company, said by email. "The challenge with duration of immunity is that those studies take time; it will likely be into 2023 before we see any results from those planned studies."

The U.S. vaccine is considered safe for rabbits at 28 days old. Rabbits have to be at least 30 days old to receive Eravac and 10 weeks old to receive Filavac.

Transition to domestic vaccine

With the emergency-use authorization for Medgene, the CVB will no longer issue new permits to import the unlicensed European vaccines, nor renew existing permits, Stepien said. Veterinarians who already have temporary permits to import vaccines can continue until their permits expire. All permits are issued for one year; the last was issued Sept. 17.

Dr. Alicia McLaughlin, a Washington veterinarian and the first practitioner to import RHDV2 vaccines, has used Filavac to vaccinate more than 1,300 rabbits at her exotics clinic north of Seattle. Most Friday mornings, she runs a vaccine clinic, and inoculates 20 to 30 rabbits.

While she is gratified to see a domestic vaccine, there are aspects of Filavac that she will miss. She likes that "Filavac has been around for a long time," she said, and that it comes with a significantly shorter window between first shot and immunity — seven versus 35 days for Medgene.

She also has concerns about the real-world impact of Medgene's two-shot requirement, she said, "especially when people are already overwhelmed because of the pandemic." She worries the need to schedule two vaccine appointments rather than one will slow the rate of vaccinations and potentially reduce the number of rabbits that are immunized overall. She said she hopes the wider availability of the Medgene vaccine might offset those potential impacts.

Dr. Linda Siperstein, who owns an exotics house-call practice in the San Francisco Bay Area, also expressed tempered excitement about the vaccine development.

"I think every vet that works with rabbits is thrilled to see a company in the U.S. producing a vaccine," she said. Siperstein has been vaccinating rabbit patients with Filavac and Eravac since May 2020.

One challenge she foresees with the U.S. product is packaging. Medgene comes in 10- or 25-dose vials that must be used within hours of being opened. Filavac and Eravac are available in multi- and single-dose vials, making them more useful for veterinarians who aren't running vaccination clinics or vaccinating groups of rabbits.

"Right now, the multi-use vials are not practical for the average vet seeing a pet rabbit," Siperstein said. She called Medgene to express her concern, and was told the company is aiming to provide single-dose vials but is hampered for the time being by supply-chain shortages.

Melby confirmed that shortages are an issue, and elaborated that the company's core focus on livestock producers adds complexity to the situation.

"Our production facility was originally set up to tailor to producers who typically order in dosage sizes of 50-250 dose vials," he said in an email. "Today most of our inventory of the RHDV2 vaccine is in 10-dose vials. To efficiently fill single-dose vials, we need to source the vials and also need to add additional equipment to support the smaller vial sizes. Supply chain lead times for both the equipment and the vials [are] significant."

Although Siperstein is not sure what she will do if she runs out of single-dose Filavac before Medgene offers them, she is sanguine. "I think we need to have a little patience while the company works out the kinks," she said.

Eric Stewart, executive director of the American Rabbit Breeders Association, said he is happy to be able to share with his members "another opportunity for protecting rabbits."

One thing he hopes won't go away in the excitement over the vaccine is vigilance around sanitation. Stewart has a fiber farm in Pennsylvania, where he raises angora rabbits and goats. As reports of RHDV2 circulated, he built a fully biosecure rabbitry for his core breeding stock. It includes an anteroom, where he can change his shoes and clothes and apply disinfectants before entering the rabbitry. The virus is highly stable and can be carried on any object it comes into contact with.

"One thing that everybody needs to keep in their minds is that no vaccine has 100% efficacy," he said. "Biosecurity measures are far more critical than vaccinating rabbits."

New chapter in rabbit medicine

In the long term, RHDV2 vaccines could do more for rabbits than protect them against a destructive virus. They may improve rabbit medicine more generally, in the opinion of some practitioners and rabbit owners.

McLaughlin pointed out that while annual vaccinations and wellness appointments are routine for many dogs and cats, until now, there have been no vaccinations for rabbits — something that is true for most exotic pets. As a result, it's far less usual for rabbit owners than cat and dog owners to bring their pets to the veterinarian for regular wellness checks. This means, McLaughlin said, that veterinarians are less likely to catch health concerns in rabbits early, when intervention is most effective.

However, an annual RHDV2 vaccine could create the basis for more routine care and, as a result, improve rabbit health overall. "It may be a positive thing," McLaughlin said, adding that she thinks the impact might be apparent in five to 10 years.

Sailer of the House Rabbit Society agrees that the RHDV2 vaccine could provide a foundation for more consistent relationships between rabbit owners and veterinarians. In turn, she said, she hopes those opportunities will spur more veterinarians to pursue advanced training in rabbit medicine.

"I think that would be really fantastic," she said. "An unintended consequence potentially, as part of this, we could get more rabbit-savvy veterinarians … and as a result, that could benefit rabbits."

Update: As of March 14, 2022, Medgene Labs lists 44 states, plus Washington D.C., where its RHDV2 vaccine can be distributed under federal emergency-use authorization.

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