January 28, 2014
At the Merial Avian Forum Asia, Dr Michel Bublot from the Global Research & Development department of Merial, also known aptly as the 'father of VAXXITEK' within the Merial team, introduced the VAXXITEK® HVT+IBD vaccine to over 250 participants, highlighting the safety and efficacy of the vaccine.
Dr Bublot set the stage by firstly illustrating problems encountered with classical modified live vaccines (MLV) against infectious bursal disease (IBD), such as poor efficacy as a result of the immunity gap, which occurs when maternally-derived antibody (MDA) level falls; safety issues including bursal damage and immunosuppression; and the efficacy of drinking water administration.
Although the immune complete IBD vaccine (ICx), which obtained USDA license in 1995, solved the problem of vaccination timing and drinking water administration, issues of bursal lesions and the immunity gap still persist.
Thankfully, Merial tapped on new technologies and developed the new IBD vaccine based on a viral vector - the herpesvirus of turkey (HVT) that is widely used as a Marek's disease vaccine. The vaccine, which offers protection against both IBD and Marek's disease, is administered at the hatchery either in-ovo or via the subcutaneous route, eliminating issues observed in the field with drinking water administration.
After more than 10 years of research and development, of which Dr Bublot was personally involved, VAXXITEK® HVT+IBD was shown to be protective against classical, variant as well as very virulent IBDV strains in chickens. The vector vaccine gained market authorisation in the EU in 2002, marking it the first replicating vector vaccine authorised in the EU. Currently, several billion doses of VAXXITEK® HVT+IBD were administered in more than 60 countries, after field tests were conducted on local broilers and layers in different regions.
Dr Bublot proceeded to illustrate the safety of this vaccine, which has been demonstrated in chickens as well as in non-target species in laboratory conditions. Among 10 live IBD vaccines (including mild, intermediate, intermediate + and ICx) tested in broilers without IBD maternally-derived antibodies (MDAs), VAXXITEK® HVT+IBD was the only vaccine that did not induce bursal lesions.
In birds with high level of MDAs, it induces rapid onset of immunity and lifelong protection after one administration. With VAXXITEK® HVT+IBD, the absence of the 'immunity gap' is also noted. The immunity gap is the time period when birds vaccinated with the classical or ICx live vaccines are not protected against IBD challenge due to the interference of MDAs. The absence of the 'immunity gap' is illustrated by the kinetics of VAXXITEK-induced anti-VP2 antibodies, which remain above the protective threshold after MDAs decrease; whereas it decreased to non-protective levels with other live vaccines. Indeed, the live vaccines (including ICx) have to replicate in the bursa before inducing antibodies and protection. MDAs delay the replication of these live vaccines strains but do not block the replication of virulent IBDV field isolates.
Importantly, Dr Bublot assured that performance observed in laboratory conditions has been confirmed worldwide in field conditions. Field trials on broilers subject to very virulent IBDV challenge have shown that VAXXITEK® HVT+IBD resulted in consistently higher levels of antibodies, which eliminate the 'immunity gap'; and higher bursa/body weight ratio than broilers vaccinated with classical intermediate IBD vaccine.
A separate trial on commercial layers subject to very virulent IBDV have shown that VAXXITEK® HVT+IBD is the only vaccine that could induce VP2 antibodies before challenge at day 42, as compared to other intermediate IBDV vaccines, making it the only vaccine that provides protection against very virulent IBDV.
Dr Bublot explained that the high efficacy of the HVT-vectored IBD vaccine is likely due to the biological properties of the HVT vector. Firstly, HVT replication and VP2 expression are not impaired by maternally-derived antibody. Moreover, the early expression of the VP2 protein is presented to the immune system, providing full immunity at week 2, resulting in the absence of the immunity gap.
Dr Bublot noted, however, that anti-VP2 antibodies can only be tested with Synbiotics ProFLOK IBD+ Elisa kit, as classical Elisa kits detect mainly anti-VP3 antibodies.
While the vaccine provides Marek's disease (MD) protection at a level equivalent to that induced by the HVT vaccine, Dr Bublot recommended that in areas where MD challenge is high, the vaccine can be combined with Rispens MD vaccine.
In conclusion, Dr Bublot said that in contrast to HVT-vectored Newcastle disease vaccines where at least one additional administration of classical live vaccine is needed for full protection; VAXXITEK® HVT+IBD can fully replace classical vaccines with a single shot at the hatchery. However, a killed IBD vaccine booster is required before the laying period solely for breeders to transmit high level of MDA in their progeny.
Further, compared to conventional vaccines, it is safe and efficacious in the absence of the 'immunity gap', without risk of bursal lesion and immunosuppression. Finally, its wide application is shown through trials on white and coloured broilers, layers and breeders.
This first edition of Merial Avian Forum in Asia, which took place in Bangkok during 3-4 September, brought together over 250 Merial partners, distributors, customers and staff from over 20 countries, including China, Pakistan, India, Bangladesh, Thailand, Indonesia, Sri Lanka, Malaysia, the Philippines, Korea and Japan.
