Medgene RHDV2 vaccine (US - conditional)

The Medgene RHDV2 vaccine represents a critical advancement in rabbit disease prevention for the United States, being the only domestically produced and USDA-approved vaccine against rabbit haemorrhagic disease virus type 2. Developed by Medgene Labs of Brookings, South Dakota, this innovative vaccine received Emergency Use Authorization from the USDA Center for Veterinary Biologics in 2021 and was subsequently granted a Conditional Use License in November 2023, marking an important milestone in protecting American rabbits from this devastating disease.

Unlike the European inactivated vaccines that rely on virus harvested from infected rabbit livers, the Medgene vaccine utilizes recombinant subunit technology based on baculovirus expression. This modern approach produces the RHDV2 VP60 capsid protein in insect cell cultures, eliminating the need for large numbers of infected rabbits in the manufacturing process. The technology not only addresses animal welfare concerns associated with traditional vaccine production but also allows for more scalable manufacturing to meet the urgent demand created by the spread of RHDV2 across the United States.

The vaccine is an inactivated (killed) product that cannot cause disease or result in viral shedding from vaccinated animals. This safety profile is particularly reassuring for rabbit owners and veterinarians dealing with an unfamiliar disease. The vaccine has demonstrated 100% efficacy in challenge studies, with all vaccinated rabbits surviving direct exposure to live RHDV2 virus, while unvaccinated control animals succumbed to infection.

Administration of the Medgene vaccine is restricted to licensed veterinarians in states where the vaccine has been authorized. This requirement ensures proper handling, storage, and administration of the vaccine, as well as appropriate record-keeping for disease surveillance purposes. Rabbit owners interested in vaccination should contact their veterinarian to discuss availability and scheduling, as the vaccine may need to be specially ordered.

The Medgene RHDV2 vaccine is indicated for protection against rabbit haemorrhagic disease caused by RHDV2 (rabbit haemorrhagic disease virus type 2) in domestic rabbits. RHDV2 first emerged in France in 2010 and was detected in the United States in 2018, with major outbreaks beginning in 2020 that spread rapidly across the country. The disease is now considered endemic in many regions of the United States, affecting both domestic pet rabbits and wild rabbit populations including cottontail rabbits and jackrabbits.

RHDV2 poses a severe threat to rabbit populations due to its high virulence and mortality rate. Infected rabbits may show clinical signs including fever, lethargy, anorexia, respiratory distress, and neurological abnormalities, though in many cases the disease progresses so rapidly that rabbits are found dead without any preceding symptoms. The virus causes acute liver failure and widespread coagulation disorders, leading to internal haemorrhaging. Unlike classical RHDV1 strains, RHDV2 affects rabbits of all ages, including young kits that would otherwise have natural age resistance.

The vaccine is recommended for all domestic rabbits in the United States, regardless of whether they are housed indoors or outdoors. The environmental stability of RHDV2 means the virus can be introduced into homes on clothing, footwear, hay, vegetables, or other contaminated materials. The virus can survive on surfaces for extended periods (over 100 days according to some research) and is resistant to many common disinfectants, making strict biosecurity measures challenging to maintain.

Veterinarians may particularly recommend vaccination for rabbits in areas with confirmed RHDV2 cases, though the ongoing spread of the virus means that geographic risk assessments are constantly evolving. The House Rabbit Society, major rabbit rescue organisations, and veterinary associations have endorsed vaccination as a critical component of rabbit healthcare in the United States.

The vaccine provides protection specifically against RHDV2 and does not protect against classical RHDV1 strains. However, since RHDV2 is the primary calicivirus threat in North America and myxomatosis is not endemic in most of the United States, this focused protection addresses the main viral disease risk for American rabbits.

The Medgene RHDV2 vaccine requires a two-dose primary vaccination series for initial immunisation, distinguishing it from some European vaccines that provide protection with a single dose. The recommended protocol involves subcutaneous injection of 0.5 ml per dose, with the second dose administered 21 days after the first. This two-dose regimen ensures robust and durable immunity against RHDV2 infection.

The minimum age for vaccination is 4-7 weeks, though most veterinarians recommend beginning vaccination at 7 weeks of age when possible. Rabbits become fully protected approximately 14 days after receiving the second dose, meaning the entire primary immunisation process requires approximately 35 days from the first injection to achieve protective status. This timeline is important to consider when planning vaccination in relation to potential exposure risks.

Following the initial two-dose series, annual booster vaccination is required to maintain protective immunity. Current guidance suggests that rabbits that have completed the primary series need only a single booster dose each year, though formal label guidance on boosters continues to evolve as more data becomes available. If more than 12 months have elapsed since the initial series or previous booster, some veterinarians recommend restarting with two doses to ensure adequate protection.

The vaccine is administered by subcutaneous injection, typically in the scruff of the neck or lateral thoracic wall. Only licensed veterinarians may administer the vaccine in most states, ensuring proper technique and appropriate patient evaluation. Before vaccination, the veterinarian will typically perform a health examination to confirm the rabbit is suitable for immunisation.

The vaccine is available in multi-dose (10-dose) vials and more recently in single-dose vials, which have improved convenience for veterinary practices and reduced waste. Multi-dose vials must be handled according to sterile technique, and while the vaccine should ideally be used immediately after opening, research has demonstrated maintained sterility over extended periods when proper aseptic technique is employed.

Veterinary practices may need to order the vaccine specially, as it may not be routinely stocked. Rabbit owners should contact their veterinarian in advance to arrange vaccination appointments and allow time for vaccine procurement.

The Medgene RHDV2 vaccine has demonstrated a favourable safety profile in clinical studies and widespread field use, with most rabbits experiencing no observable adverse effects. When side effects do occur, they are typically mild and self-limiting. The vaccine's safety record has been a key factor in its successful deployment during the RHDV2 emergency in the United States.

The most commonly reported side effect is a small localised swelling at the injection site. This reaction represents the normal inflammatory response to the vaccine and typically resolves within a few days to weeks without treatment. Owners should be advised that a small lump at the injection site is expected and not cause for concern unless it grows significantly, becomes painful, or shows signs of infection such as redness, heat, or discharge.

Some rabbits may develop a slight temporary fever following vaccination, though this is usually mild and resolves without intervention within 24-48 hours. Transient lethargy is another commonly reported effect, with some rabbits appearing somewhat less active than usual for several hours following their vaccination appointment. This may partly reflect the stress of visiting the veterinary clinic rather than a direct vaccine effect.

Reduced appetite for a short period following vaccination has been reported in some cases. While mild appetite reduction is typically not concerning, any rabbit that stops eating entirely or shows signs of gastrointestinal distress should be evaluated promptly. Rabbit owners should be counselled to monitor their rabbit's eating and faecal output following vaccination and contact their veterinarian if normal patterns are not resumed within 24 hours.

Serious adverse reactions to the Medgene vaccine have been rare in post-marketing surveillance. As with any vaccine, severe allergic reactions are theoretically possible, though reports of such reactions have been uncommon. Signs of serious allergic reaction would include facial swelling, difficulty breathing, collapse, or severe acute lethargy. Any such symptoms require immediate veterinary attention.

The inactivated nature of the vaccine means there is no possibility of vaccine-induced disease or viral shedding from vaccinated animals, providing reassurance about safety for household contacts.

Several contraindications should be considered before administering the Medgene RHDV2 vaccine to ensure patient safety and optimal immune response. As with all vaccines, administration should be restricted to healthy animals. Rabbits that are currently ill, stressed, immunocompromised, or debilitated should not be vaccinated until their condition has resolved. Underlying illness can impair the immune response to vaccination and may be worsened by the physiological stress of the vaccination process.

Rabbits with known hypersensitivity to the vaccine components should not receive the Medgene vaccine. While severe allergic reactions have been rare, any rabbit that experienced a significant adverse reaction to a previous dose should be carefully evaluated before receiving additional doses. Alternative protective strategies, such as enhanced biosecurity measures, may need to be considered for such individuals.

The vaccine has not been specifically studied in pregnant or lactating does, and the influence on fertility has not been formally investigated. While the inactivated nature of the vaccine suggests a low likelihood of adverse reproductive effects, vaccination of pregnant animals should be performed with caution and only when the veterinarian determines that the benefits clearly outweigh potential risks. Pregnant does should be handled carefully during vaccination to minimise stress.

The minimum age for vaccination is typically considered to be 4-7 weeks, though some sources specify 7 weeks as the minimum age for routine vaccination. Vaccination of very young kits may be affected by maternal antibodies if the dam was previously vaccinated. Veterinarians may recommend different timing based on individual circumstances.

As the vaccine is only available through licensed veterinarians, it is not available in states that have not authorised its use. Rabbit owners in states without current authorisation should contact their state veterinarian's office for guidance on vaccine availability. The list of authorised states has expanded significantly since initial release, with most states now permitting vaccine use.

No specific information is available regarding interactions with other vaccines or medications, and decisions to use the Medgene vaccine in conjunction with other treatments must be made on a case-by-case basis.

Formal drug interaction studies have not been conducted for the Medgene RHDV2 vaccine, and specific data on concurrent use with other veterinary medicinal products is limited. As with most vaccines, decisions to administer the Medgene vaccine alongside other medications must be made on an individual basis by the attending veterinarian, considering the overall health status of the rabbit and the relative benefits and risks.

Rabbits that have previously received European RHDV2 vaccines such as Filavac or Eravac may still require the full two-dose Medgene series when transitioning to the domestically produced vaccine. Cross-protection between different vaccine formulations has not been formally established, and veterinary guidance from major rabbit rescue organisations recommends completing the full primary series regardless of previous vaccination with other products.

Immunosuppressive medications such as corticosteroids could potentially interfere with the development of adequate immune responses to vaccination. Rabbits receiving immunosuppressive therapy should ideally complete their treatment and recover normal immune function before vaccination. If vaccination cannot be delayed due to high disease risk, the veterinarian should consider that vaccine efficacy may be reduced.

Non-steroidal anti-inflammatory drugs commonly used in rabbit medicine, such as meloxicam, are not known to significantly interfere with vaccine responses. However, because NSAIDs can mask fever and other early signs of adverse reactions, some veterinarians may prefer to avoid concurrent administration unless pain management is specifically indicated for another condition.

Probiotic supplements and gastrointestinal support products frequently used in rabbit care are not expected to interact with the vaccine. However, rabbit owners should inform their veterinarian about all supplements and medications their rabbit is receiving to allow comprehensive evaluation of potential interactions.

The vaccine does not contain a traditional adjuvant system like the European inactivated vaccines, which may reduce the potential for interactions with other adjuvanted products. However, spacing out administration of multiple vaccines when feasible remains a prudent approach.

Antibiotic treatments do not typically interfere with vaccine responses, though rabbits requiring antibiotics may be systemically unwell and vaccination might be better deferred until recovery.

Several important precautions and warnings should be observed when using the Medgene RHDV2 vaccine to ensure safe and effective outcomes. The foremost precaution is that only healthy rabbits should be vaccinated. A thorough clinical examination by the administering veterinarian is essential to identify any underlying conditions that might contraindicate vaccination or impair the immune response. Rabbits should be alert, eating normally, and showing no signs of illness at the time of vaccination.

The vaccine is currently under Conditional Use License from the USDA, which means that while safety and efficacy criteria have been satisfied, ongoing monitoring and data collection continue. Veterinarians administering the vaccine must comply with USDA reporting requirements and maintain appropriate records. This conditional status does not indicate concerns about vaccine safety but reflects the regulatory pathway for rapidly deployed vaccines during disease emergencies.

Administration is restricted to licensed veterinarians in states that have authorised vaccine use through their state veterinarian's office. This requirement ensures appropriate professional oversight, proper handling and storage, and accurate record-keeping for disease surveillance purposes. Rabbit owners cannot purchase or administer the vaccine themselves and must work with their veterinary practice to schedule vaccinations.

The vaccine provides protection specifically against RHDV2 and does not protect against classical RHDV1 strains or myxomatosis. While RHDV1 is not currently a significant concern in most of the United States, and myxomatosis is not endemic, rabbit owners should be aware of the specific protection scope. Rabbits travelling internationally or being imported from other countries may require additional vaccinations based on the disease risks in those regions.

Proper cold chain maintenance is essential for vaccine potency. The vaccine must be stored refrigerated between 2°C and 8°C and protected from freezing. Veterinary practices should verify proper storage conditions before administration. Any vaccine that may have been improperly stored should not be used.

Owners should be counselled about expected post-vaccination effects and when to contact their veterinarian. Normal responses may include mild lethargy, slight swelling at the injection site, and reduced activity for 24-48 hours. More serious symptoms including complete loss of appetite, signs of allergic reaction, or any concerning changes warrant immediate veterinary consultation.

Proper storage and handling of the Medgene RHDV2 vaccine is essential to maintain potency and ensure effective protection for vaccinated rabbits. The vaccine must be stored under refrigerated conditions at temperatures between 2°C and 8°C (approximately 35°F to 46°F). Maintaining the cold chain throughout distribution and storage at the veterinary practice is critical, as temperature excursions can compromise vaccine viability and potentially result in inadequate protection for vaccinated animals.

The vaccine must not be frozen. Freezing can cause irreversible damage to the vaccine's structure and immunogenic properties. Any vaccine that is suspected of having been exposed to freezing temperatures should not be used. Similarly, extended exposure to temperatures above the recommended refrigeration range can cause degradation of vaccine components.

The vaccine vials should be protected from light during storage. Exposure to ultraviolet radiation or prolonged ambient light can degrade vaccine components over time. Storing vials in their original packaging or in a light-protected container within the refrigerator helps maintain stability.

The shelf life of the Medgene vaccine is 24 months from the date of manufacture when stored under appropriate conditions. Veterinary practices should check expiration dates before administration and implement first-in-first-out stock rotation to ensure vaccines are used before expiration. The expiration date is marked on the vial labelling and should be verified before each use.

Once opened, multi-dose vials should ideally be used immediately according to the label instructions. However, research conducted on vaccine sterility has demonstrated that when collected with appropriate aseptic precautions, the vaccine may maintain sterility for extended periods. Single-dose vials, now available, eliminate concerns about multi-dose vial handling and reduce waste in practices with lower rabbit patient volumes.

Disposal of unused vaccine and vaccine waste should follow local regulations for biological materials. Used needles and syringes should be disposed of in appropriate sharps containers. Personnel handling the vaccine should observe standard hygiene precautions, and accidental self-injection should be avoided. While the vaccine is not considered hazardous to human health, medical advice should be sought in the event of accidental injection.

The Medgene RHDV2 vaccine has been developed and tested for use across all breeds of domestic rabbits, with no breed-specific contraindications identified. Clinical trials were conducted using New Zealand White rabbits, a standard laboratory and commercial meat breed, but extensive field use has demonstrated safety and efficacy across the diverse range of pet rabbit breeds common in the United States.

Dwarf breeds including Netherland Dwarf, Holland Lop, Mini Rex, Mini Lop, Lionhead, and Polish rabbits receive the same vaccine dose as larger breeds. The immunological response to vaccination is determined by the antigenic content rather than body weight, so no dose adjustment is required for small rabbits. However, particular attention should be paid to injection technique in very small rabbits to ensure proper subcutaneous placement and minimise discomfort.

Giant breeds such as Flemish Giant and Continental Giant do not require increased vaccine doses. The standard 0.5 ml dose provides adequate antigenic stimulation regardless of body size. Owners of giant breeds should be informed that localised injection site reactions may appear proportionally smaller relative to their rabbit's body size but still warrant appropriate monitoring.

Lop-eared breeds including Holland Lop, Mini Lop, English Lop, and French Lop require standard vaccination protocols with no special modifications needed. The subcutaneous injection site in the scruff or lateral thoracic wall is not affected by ear conformation.

Breeds with distinctive coat characteristics such as Rex (with their plush velvet-like fur), Angora (with long wool), and Lionhead (with mane-like fur around the head) may require careful fur parting to visualise the skin for injection. Ensuring proper needle placement into the subcutaneous space is important regardless of coat type.

Age considerations apply across all breeds. While the minimum age is generally considered 4-7 weeks, many veterinarians recommend beginning vaccination at 7 weeks when possible. Senior rabbits should continue to receive vaccination, as protection against RHDV2 remains important throughout life. Elderly rabbits may have somewhat reduced immune responses, but vaccination still provides meaningful protection.

The Medgene vaccine is currently the only RHDV2 vaccine approved for use in the United States, making it the primary option for American rabbit owners seeking protection against this disease. However, understanding related vaccines used internationally provides context for comprehensive rabbit health management and is relevant for rabbits that may have been previously vaccinated abroad or that will travel internationally.

Eravac is an inactivated adjuvanted vaccine produced by Hipra Laboratories of Spain that provides protection against RHDV2. Like the Medgene vaccine, it targets specifically RHDV2 and does not protect against RHDV1 or myxomatosis. Eravac has been used in the United States under special import permits during the RHDV2 emergency, though the availability of the domestic Medgene vaccine has largely superseded the need for imported products. Eravac uses traditional inactivated virus technology rather than recombinant subunit production.

Filavac VHD K C+V is another European vaccine, manufactured by Filavie Laboratories of France, that provides bivalent protection against both RHDV1 and RHDV2. This vaccine has been imported into the United States under special permits and has been used in Canada as well. The broader coverage against both calicivirus types may be relevant for international travel or import scenarios.

Nobivac Myxo-RHD PLUS is a live recombinant vector vaccine from MSD Animal Health that provides protection against myxomatosis, RHDV1, and RHDV2. This vaccine is not available in the United States because it is a live genetically modified product that cannot be imported under current regulations. However, rabbit owners should be aware of its existence for international travel planning.

For American rabbit owners, the Medgene vaccine remains the recommended and most accessible option for RHDV2 protection. The vaccine's domestic production ensures reliable availability without the complications of international importation. Rabbit owners should work with their veterinarian to ensure their rabbits receive appropriate vaccination and discuss any special circumstances such as travel or prior international vaccination that might affect their rabbit's protection strategy.