Combination Myxo-RHD vaccines (Nobivac)

Nobivac Myxo-RHD PLUS represents a significant advancement in rabbit preventive medicine, offering comprehensive protection against three of the most devastating viral diseases affecting domestic rabbits. This live recombinant vector vaccine, manufactured by MSD Animal Health, provides immunity against myxomatosis and rabbit haemorrhagic disease caused by both classical (RHDV1) and variant (RHDV2) strains through a single annual injection. The vaccine was licensed by the European Medicines Agency in 2019 and has become the gold standard for rabbit vaccination protocols throughout Europe and the United Kingdom.

The vaccine utilizes innovative recombinant vector technology, employing attenuated myxoma virus strains that have been genetically modified to express the VP60 capsid proteins from both RHDV1 and RHDV2. This sophisticated approach allows the vaccine to stimulate robust immunity against all three pathogens simultaneously without requiring multiple injections or the use of adjuvants. The vaccine contains two distinct myxoma vectored strains: strain 009 (expressing RHDV1 capsid protein) and strain MK1899 (expressing RHDV2 capsid protein), each present at concentrations of 10^3.0 to 10^5.8 focus forming units per dose.

Nobivac Myxo-RHD PLUS is supplied as a lyophilisate (freeze-dried powder) that must be reconstituted with the provided solvent before administration. The reconstituted vaccine appears as an off-white or cream-coloured suspension and should be used immediately after preparation. The vaccine is administered as a single subcutaneous injection, making it considerably more convenient than previous vaccination protocols that required separate injections for myxomatosis and RHD protection.

As with all vaccines, administration should only be performed by or under the direction of a rabbit-savvy veterinarian who can ensure the rabbit is healthy enough for vaccination and can properly evaluate the vaccination history. The importance of veterinary oversight cannot be overstated, as factors such as previous vaccination status, exposure to natural myxomatosis infection, and the phenomenon of vector interference can significantly impact vaccine efficacy. Annual boosters are required to maintain protective immunity throughout the rabbit's life.

Nobivac Myxo-RHD PLUS is indicated for the active immunisation of rabbits to reduce mortality and clinical signs associated with three major viral diseases. The primary indication is prevention of myxomatosis, a highly fatal disease caused by myxoma virus that is endemic throughout Europe, the United Kingdom, and Australia. Myxomatosis spreads primarily through biting insects such as fleas, mosquitoes, and other arthropod vectors, making all rabbits potentially susceptible regardless of whether they are housed indoors or outdoors. Without vaccination, mortality rates from myxomatosis can approach 100% in unprotected rabbit populations.

The second major indication is protection against classical rabbit haemorrhagic disease caused by RHDV1 strains. This calicivirus causes acute necrotising hepatitis and widespread coagulopathy, leading to haemorrhages in multiple organs and extremely high mortality rates. RHDV1 typically causes peracute or acute disease with death occurring within 12-72 hours of infection. The virus is highly stable in the environment, surviving for extended periods on surfaces, in soil, and on fomites, making environmental contamination a significant concern.

The third indication addresses the emerging threat of RHDV2, a variant strain first identified in France in 2010 that has since spread throughout Europe and beyond. RHDV2 differs from classical RHDV1 in several important ways: it affects rabbits of all ages including young kits under 6 weeks old, it may cause a more protracted disease course, and crucially, vaccines against RHDV1 do not provide reliable cross-protection against RHDV2. The emergence of RHDV2 necessitated the development of Nobivac Myxo-RHD PLUS to replace the original Nobivac Myxo-RHD vaccine, which only protected against RHDV1.

The vaccine is recommended for all domestic rabbits regardless of their living situation. Indoor rabbits are not exempt from risk, as myxoma virus can be carried inside on clothing, other pets, or insects, while caliciviruses can be introduced on food, hay, or other contaminated materials. The vaccine is particularly critical in areas where wild rabbit populations are present, as they serve as reservoirs for all three diseases.

Veterinarians may also recommend this vaccine for rabbits in breeding programs, rescue centres, boarding facilities, and show environments where exposure risk is heightened. The single-injection convenience of Nobivac Myxo-RHD PLUS has significantly improved vaccination compliance rates compared to previous protocols requiring multiple separate vaccinations.

The dosage and administration protocol for Nobivac Myxo-RHD PLUS has been carefully established to provide optimal protection while minimizing stress on the rabbit patient. The vaccine is administered as a single dose of either 0.2 ml or 0.5 ml (depending on the presentation) given by subcutaneous injection. The standard primary vaccination schedule begins from 5 weeks of age, though the full 12-month duration of immunity is only achieved when vaccination occurs from 7 weeks of age onwards.

For rabbits vaccinated at 5-6 weeks of age, revaccination at 7 weeks or later is recommended to ensure the full duration of immunity is achieved. This early vaccination option is particularly valuable in high-risk situations such as disease outbreaks or when young rabbits must be rehomed before they reach 7 weeks of age. The onset of immunity occurs approximately 3 weeks after vaccination, which is an important consideration when timing vaccination in relation to potential disease exposure.

The vaccine must be reconstituted immediately before use by adding the provided solvent to the lyophilisate vial. The reconstituted vaccine should be gently mixed until the pellet is completely dissolved, producing an off-white or cream-coloured suspension. Once reconstituted, the vaccine must be used immediately and any unused material discarded appropriately. The vaccine should not be mixed with any other veterinary medicinal products.

Subcutaneous injection is performed by lifting a fold of loose skin, typically over the scruff of the neck or the lateral thoracic wall, and inserting the needle into the space beneath the skin but above the underlying muscle. Standard aseptic technique should be employed, including appropriate skin preparation. The injection site should be monitored for any adverse reactions in the days following vaccination.

Annual revaccination is required to maintain protective immunity. Booster vaccinations should be administered at 12-month intervals, though veterinarians may recommend more frequent vaccination in very high-risk situations. If a rabbit's vaccination status has lapsed significantly beyond the 12-month interval, the veterinarian may recommend additional precautions such as prior vaccination with an inactivated RHDV2 vaccine to overcome potential vector interference issues.

It is essential that vaccination is only performed by a qualified veterinary professional who can conduct a thorough health examination prior to administration. Vaccination should only be administered to healthy rabbits, and any animals showing signs of illness, immunosuppression, or stress should be deferred until their condition has resolved.

Nobivac Myxo-RHD PLUS has an established safety profile based on extensive clinical studies and years of field use, though as with any vaccine, adverse reactions can occur. The most commonly observed side effect is a temporary localised reaction at the injection site, which may present as a small swelling of 1-2 cm in diameter. This reaction typically appears within the first week following vaccination and generally resolves spontaneously without treatment within a few weeks. Injection site reactions are reported as occurring very commonly in clinical studies.

A transient increase in body temperature is another commonly reported side effect. Studies have documented temperature elevations of up to 1°C occurring in the days following vaccination. This mild fever is typically self-limiting and resolves within a few days without intervention. Rabbit owners should be advised that their pet may appear slightly less active than usual for 24-48 hours post-vaccination, which is a normal physiological response to immune system activation.

Some rabbits may develop small pox-like lesions on the face or ears, particularly around the injection site, in the weeks following vaccination. When these lesions are very localised and resolve without spreading, they are considered consistent with the expected immune response and do not indicate vaccine failure or infection. However, owners should be advised to monitor their rabbit closely and report any lesions that appear to spread or worsen.

More serious adverse reactions are rare but can include hypersensitivity or allergic reactions. Signs of a serious allergic reaction may include facial swelling, difficulty breathing, collapse, or severe lethargy. Any rabbit exhibiting these symptoms following vaccination requires immediate veterinary attention. Anaphylactic reactions, while extremely rare, can be life-threatening and veterinary practices should have appropriate emergency medications available.

It is important to monitor vaccinated rabbits for any changes in appetite, behaviour, or faecal output in the days following vaccination. While significant gastrointestinal disturbance is not typically associated with this vaccine, any rabbit that stops eating or shows signs of GI stasis following vaccination should be evaluated promptly. Rabbit owners should be counselled to contact their veterinarian if any concerning symptoms develop or persist beyond the expected timeframe for normal post-vaccination effects.

Several important contraindications must be considered before administering Nobivac Myxo-RHD PLUS to ensure patient safety and vaccine efficacy. The vaccine is contraindicated in rabbits with known hypersensitivity to the active substances, to any of the excipients, or to residues from manufacture. Rabbits that have experienced allergic reactions to previous vaccinations should be carefully evaluated before receiving this vaccine, and alternative vaccination strategies may need to be considered.

Vaccination should only be administered to healthy animals. Rabbits that are currently ill, stressed, or immunocompromised should not receive the vaccine until their condition has resolved. This includes rabbits recovering from surgery, those being treated with immunosuppressive medications, or animals suffering from concurrent infections. Administering vaccines to sick animals may result in inadequate immune responses or could potentially worsen the animal's condition.

Pregnant does represent a special consideration. While safety studies have been conducted in pregnant rabbits without evidence of adverse effects on pregnancy or offspring, vaccination of pregnant animals should be performed with caution and only when the benefits clearly outweigh any potential risks. Ideally, breeding does should be vaccinated before breeding to ensure protective immunity is established prior to pregnancy.

A particularly important contraindication relates to rabbits with prior vaccination history using other myxomatosis vaccines. The phenomenon of vector interference means that rabbits previously vaccinated with other myxomatosis vaccines, or those that have experienced natural myxomatosis infection, may not develop an adequate immune response against rabbit haemorrhagic disease following vaccination with Nobivac Myxo-RHD PLUS. This occurs because pre-existing immunity to the myxoma virus vector can limit vaccine virus replication and reduce expression of the RHDV antigens. Veterinarians should carefully review vaccination history and consider strategies to overcome vector interference when indicated.

Rabbits under 5 weeks of age should not be vaccinated as safety and efficacy have not been established in this age group. Additionally, the vaccine should not be used in combination with other vaccines unless specific compatibility has been established.

Understanding potential interactions between Nobivac Myxo-RHD PLUS and other medications or vaccines is essential for optimal patient care. Currently, no specific data is available regarding the safety and efficacy of this vaccine when used concurrently with other veterinary medicinal products. Therefore, decisions to administer this vaccine before or after other medications must be made on a case-by-case basis by the attending veterinarian, weighing the risks and benefits in each individual situation.

The most significant interaction consideration relates to other myxomatosis vaccines or products. As discussed, the vector interference phenomenon can significantly impact vaccine efficacy in rabbits that have received other myxomatosis vaccines. When transitioning rabbits from older vaccination protocols to Nobivac Myxo-RHD PLUS, veterinarians may recommend administering an inactivated RHDV2 vaccine (such as Filavac or Eravac) first to prime the immune system against RHDV2 before giving Nobivac Myxo-RHD PLUS. This strategy helps ensure adequate protection against all three diseases.

Immunosuppressive medications such as corticosteroids may interfere with the development of adequate immune responses to vaccination. Rabbits receiving immunosuppressive therapy should ideally complete their treatment course and recover normal immune function before vaccination. If vaccination cannot be delayed, the veterinarian should consider the potential for reduced vaccine efficacy and may recommend serological testing to confirm immune response or earlier revaccination.

Antibiotics and other antimicrobial treatments do not typically interfere with vaccine efficacy, as the vaccine relies on viral replication rather than bacterial processes. However, rabbits requiring antibiotic treatment may be systemically unwell, and vaccination should generally be deferred until the rabbit has recovered from the underlying condition necessitating antibiotic therapy.

Non-steroidal anti-inflammatory drugs (NSAIDs) such as meloxicam, commonly used for pain management in rabbits, are not known to significantly interfere with vaccine responses. However, as these medications can potentially mask early signs of adverse reactions, veterinarians may advise avoiding routine NSAID administration immediately following vaccination unless specifically indicated for pain management.

Several important precautions and warnings must be considered when using Nobivac Myxo-RHD PLUS to ensure safe and effective vaccination outcomes. First and foremost, only healthy rabbits should be vaccinated. A thorough pre-vaccination health examination by a qualified veterinarian is essential to identify any underlying conditions that might contraindicate vaccination or affect vaccine efficacy. This examination should assess body condition, hydration status, respiratory function, and overall demeanour.

The phenomenon of vector interference deserves particular attention as a critical warning. Rabbits that have been previously vaccinated with another myxomatosis vaccine, or that have experienced natural myxomatosis infection in the field, may not develop an adequate immune response against rabbit haemorrhagic disease following vaccination. This is because the immune system's response to the familiar myxoma virus vector can limit vaccine virus replication, preventing adequate expression of the RHDV antigens. Veterinarians should carefully document vaccination history and consider appropriate strategies to address vector interference when indicated.

Accurate recording of vaccination details is essential for proper monitoring and follow-up care. Documentation should include the date of vaccination, vaccine batch number, route of administration, injection site, and any immediate reactions observed. This information is critical for tracing in the event of adverse reactions or disease outbreaks and for planning future vaccinations.

The vaccine should be handled and stored according to manufacturer specifications to maintain potency. It must be stored and transported refrigerated at 2°C to 8°C and protected from light. Freezing must be avoided as it can damage the vaccine. Once reconstituted, the vaccine must be used immediately. Any unused reconstituted vaccine should be disposed of appropriately according to local regulations.

Owners should be counselled about what to expect following vaccination and when to seek veterinary attention. Normal post-vaccination effects may include mild lethargy, slight reduction in appetite, and small localised swelling at the injection site. However, any signs of allergic reaction, spreading skin lesions, persistent lethargy, complete loss of appetite, or other concerning symptoms should prompt immediate veterinary consultation.

Proper storage and handling of Nobivac Myxo-RHD PLUS is crucial to maintain vaccine potency and ensure effective protection for vaccinated rabbits. The vaccine lyophilisate and solvent must be stored and transported under refrigerated conditions at 2°C to 8°C. Maintaining the cold chain throughout distribution and storage is essential, as temperature excursions outside this range can compromise vaccine viability. The vaccine should never be frozen, as freezing can cause irreversible damage to the vaccine components.

The vaccine vials should be kept in the outer carton to protect them from light, as exposure to light can degrade the vaccine over time. When stored correctly, the shelf life of the unopened product is typically two years from the date of manufacture. Veterinary practices should implement first-in-first-out stock rotation to ensure vaccines are used before their expiration date. The expiry date is clearly marked on both individual vials and outer packaging.

Reconstitution should only be performed immediately before administration. The solvent should be added to the lyophilisate vial using aseptic technique, and the vial should be gently swirled or rolled until the freeze-dried pellet is completely dissolved. Vigorous shaking should be avoided as this can damage the vaccine. The reconstituted vaccine should appear as an off-white or cream-coloured suspension. Any vaccine that appears discoloured, contains particles, or appears abnormal in any way should not be used.

Once reconstituted, the vaccine has no shelf life and must be used immediately. Any unused reconstituted vaccine cannot be stored and must be disposed of appropriately. Disposal of 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. While the vaccine is not considered hazardous to human health under normal handling conditions, accidental self-injection should be avoided. In the event of accidental injection, medical advice should be sought immediately and the product information sheet should be shown to the attending physician.

Nobivac Myxo-RHD PLUS has been developed and tested for use across all breeds of domestic rabbits, and no breed-specific contraindications have been identified. However, certain breed characteristics may warrant additional consideration during vaccination to ensure optimal outcomes. The vaccine's safety profile has been established in studies using both commercial meat breeds such as New Zealand White and typical pet breeds including Dutch Belted rabbits, demonstrating broad applicability across the domestic rabbit population.

Dwarf breeds such as Netherland Dwarf, Holland Lop, and Mini Rex require particular attention to injection technique due to their small body size. In very small rabbits, the veterinarian must ensure appropriate needle placement for subcutaneous injection, avoiding inadvertent intramuscular administration or injection into excessively thin skin folds. Despite their small size, these breeds receive the same vaccine dose as larger rabbits, as the immunological response is determined by the antigen content rather than body mass.

Giant breeds including Flemish Giant, Continental Giant, and British Giant rabbits do not require dose adjustments. The standard single dose provides adequate antigenic stimulation regardless of body size. However, giant breed owners should be counselled that the standard injection site reactions may be proportionally less noticeable in these larger animals, and careful monitoring is still required.

Lop-eared breeds require standard vaccination protocols, though owners should be advised to monitor for any lesions around the ears following vaccination, as pox-like lesions occasionally develop in these areas as part of the normal immune response. The pendulous ears of lop breeds may make such lesions less immediately visible, so thorough examination is important during post-vaccination monitoring.

Age considerations apply equally across all breeds. Young rabbits should ideally be vaccinated from 7 weeks of age to achieve the full 12-month duration of immunity. Elderly rabbits may have somewhat reduced immune responses, though vaccination remains recommended as protection against these fatal diseases remains critically important throughout life. Senior rabbits with concurrent health conditions should be evaluated individually to determine appropriate vaccination timing.

Several related vaccines are available for protection against myxomatosis and rabbit haemorrhagic disease, each with distinct characteristics that may make them more suitable in specific situations. Eravac is an inactivated adjuvanted vaccine specifically targeting RHDV2 and is often used in conjunction with other vaccines when rapid RHDV2 protection is needed. Eravac has a faster onset of immunity (7 days) compared to Nobivac Myxo-RHD PLUS (3 weeks), making it valuable during outbreak situations. However, it does not protect against myxomatosis or RHDV1.

Filavac VHD K C+V is another inactivated adjuvanted vaccine that provides protection against both RHDV1 and RHDV2 but not myxomatosis. Like Eravac, it has a 7-day onset of immunity and is produced using inactivated virus derived from infected rabbit liver tissue. Both Filavac and Eravac may be recommended prior to Nobivac Myxo-RHD PLUS in situations where vector interference is a concern, as priming the immune system against RHDV2 with an inactivated vaccine can help overcome this issue.

In the United States, where myxomatosis is not endemic and Nobivac vaccines are not available, the Medgene RHDV2 vaccine provides protection specifically against RHDV2. This recombinant subunit vaccine uses different technology, employing baculovirus expression to produce viral capsid proteins without requiring infected rabbits for manufacture. It requires a two-dose primary series administered 21 days apart.

The choice between these vaccines depends on multiple factors including geographic location, disease prevalence, vaccination history, and urgency of protection needed. In the UK and Europe where all three diseases are present, Nobivac Myxo-RHD PLUS remains the cornerstone of rabbit vaccination programs due to its comprehensive protection and convenient single annual injection. However, veterinarians may recommend supplemental vaccination with RHDV2-specific vaccines in certain situations, particularly in areas experiencing active outbreaks or when transitioning rabbits from older vaccination protocols. All vaccination decisions should be made in consultation with a rabbit-savvy veterinarian who can assess individual circumstances and design an appropriate vaccination strategy.