Nobivac^® Myxo-RHD PLUS Questions and Answers

Nobivac Myxo-RHD PLUS is a vectored vaccine, which provides 3 in 1 coverage against myxomatosis, classic and variant strains of Rabbit Haemorrhagic Disease (RHD), ensuring rabbits are immunised against both common strains of RHD.

An emerging variant strain of Rabbit Haemorrhagic Disease (RHD-2) was discovered in 2010 in France and has since become widespread in the UK. Further research and pharmacovigilance demonstrated that vaccination with classic (RHD-1) strains does not provide reliable immunity against the variant RHD-2 strains.

Nobivac Myxo-RHD PLUS includes two RHD-vectored myxoma strains to provide comprehensive immunity against myxomatosis, and both classic and variant RHD.

Nobivac Myxo-RHD PLUS provides broad cover against myxoma virus and both RHD-1 and RHD-2 from a single vaccine using the same recombinant vector technology present in Nobivac Myxo-RHD. The vaccine contains a similar amount of classic strain vector to Nobivac Myxo-RHD, ensuring no reduction of antigenicity against this component.

A convenient single dose given from 7 weeks of age provides protection against all 3 pathogens with a minimum duration of immunity of 12 months.

The vaccine has a number of advantages/benefits:

1.      Vaccinates against both field strains of RHD

- contains equal quantities of both myxoma-virus vectored classic RHD-1 and variant RHD-2 strains. Both strains use VP 60 capsid genes.

2.      No adjuvant is required as it is a live vectored vaccine

3.      Lower volume to administer compared to Nobivac Myxo-RHD

- reconstituted with 0.5 ml of vaccine solvent rather than 1 ml

4.      May be given from 5 weeks of age 

- however, to avoid a reduction duration of immunity caused by MDA in some rabbits, vaccination after 7 weeks of age is recommended

5.      Approved for use during pregnancy

The onset of immunity following Nobivac Myxo-RHD PLUS is 3 weeks.

The safety profile is very similar to the current Nobivac Myxo-RHD product. The listed adverse reactions are:

A transient temperature increase of 1 – 2 °C can commonly occur. A small, non-painful swelling (maximum 2 cm diameter) at the injection site is commonly observed within the first two weeks after vaccination. The swelling will resolve completely by 3 weeks after vaccination. In pet rabbits, local reactions at the injection site such as necrosis, scabs, crusts or hair loss may occur in very rare cases. Serious hypersensitivity reactions, which may be fatal, may occur after vaccination in very rare cases. The appearance of mild clinical signs of myxomatosis may occur within 3 weeks of vaccination in very rare cases. Recent or latent infection with field myxoma virus seems to play a role in this to a certain extent.

The frequency of adverse reactions is defined using the following convention:

• very common (more than 1 in 10 animals treated displaying adverse reaction(s))
• common (more than 1 but less than 10 animals in 100 animals treated)
• uncommon (more than 1 but less than 10 animals in 1,000 animals treated)
• rare (more than 1 but less than 10 animals in 10,000 animals treated)
• very rare (less than 1 animal in 10,000 animals treated, including isolated reports)

This statement refers to a phenomenon known as vector interference. In the case of Nobivac Myxo-RHD, the vector virus is an attenuated myxoma virus strain which is modified by inclusion of a nucleic acid sequence which codes for the RHDV capsid protein and the removal of virulence factors.

Within Nobivac Myxo-RHD PLUS there are two vector constructs, one with the capsid sequence from RHDV-1 and a second from RHDV-2. Replication of these viruses within cells will therefore induce humoral and cell-mediated immunity to myxomatosis, RHDV-1 and RHDV-2.

Vector interference occurs when the level of pre-existing immunity to the vector virus is sufficient to limit the level of vaccine virus replication, preventing adequate expression of vectored antigens to stimulate priming immunity. Typically, this has been observed when using a novel myxoma-vectored RHD vaccine when there is already strong immunity to myxomatosis induced by previous vaccination (or potentially by field challenge) i.e. as occurred when Nobivac Myxo was superceded by Nobivac Myxo-RHD. In such an instance, if immunity against RHD has not already been primed, an effective RHD response may be blocked.

Now hat Nobivac Myxo RHD has left the market and all rabbits are receiving the Nobivac Myxo RHD PLUS vaccine, the priming issue associated with previous myxomatosis vaccination will no longer be a problem and a single vaccine will suffice.

Nobivac Myxo-RHD PLUS is a single dose vaccine so a single dose should immunise at any stage, however immunity has only been assessed up to 12 months. The licensed minimum duration of immunity is 12 months.

Within our 12 month duration of immunity studies, a few pox-like lesions on face or ears were seen, and provided these are very localised we feel these can be consistent with the expected immunity. Since 2011, in the majority of cases where myxomas are seen in the first three weeks post vaccination with Nobivac Myxo-RHD, we can demonstrate co-infection of the pet rabbit with both the vaccine strain (exposure during vaccination) and a field strain of myxoma virus. In studies, field strains appear to be able to form distinct but limited lesions on newly vaccinated rabbits whilst vaccinal protection is still developing.

No, the minimum age is determined by the age rather than the weight for vaccines. Safety trials for the vector virus were conducted in Netherland dwarfs for Nobivac Myxo-RHD, and these studies are appropriate to the new vaccine since formulation-wise the two products are similar enough to inform on safety.

From 7 weeks for the full duration of immunity for 12 months. It can be used from 5 weeks old if an individual requires earlier protection, however you would need to repeat the vaccine at 7 weeks old in order to get the full duration of immunity.