Vaccination is one of the most effective and cost-efficient strategies for preventing disease in humans and animals alike. Advances in vaccine technology in veterinary health can spill over into the vaccine design for human health. A good example of this is vectored vaccines. These have been successfully developed and deployed to control disease in poultry and other species. The principle behind them shows great promise for human medicine too.

All vaccines must meet some fundamental standards. In the case of vaccines for poultry, the key success factors are:

• They must be safe and able to induce a protective immune response even in the presence of maternal antibodies
• For practical purposes, they must be effective with a single dose and applicable by mass vaccination methods
• In terms of the poultry farmer’s business, they must be cost effective

Conventional veterinary vaccines that are based on attenuated or inactivated pathogens meet some of these requirements. But they also have disadvantages: in some cases, they can cause adverse reactions, particularly in young chickens, and they can also be less effective if there are maternal antibodies present.

The Trojan horse vaccine technology

Vectored vaccines work very differently from conventional vaccines and overcome many of these disadvantages. “A vectored vaccine is a bit like a Trojan horse – it provides protection against a pathogen by using a non-pathogenic agent as a vector to carry protective genes from the pathogen,” explains Michel Bublot, Global Project Leader at Global Innovation, Boehringer Ingelheim Animal Health and lead author of the new review article recently published in the reference work Viral Vectors in Veterinary Vaccine Development.

In order to produce this type of vaccine, the protective gene is cloned and inserted into the genome of the vector. The vector acts like a shuttle to deliver the foreign proteins. By mimicking natural infection, it induces an immune response in the body.

Vectored vaccines have several advantages over conventional vaccines:

• They do not generally cause adverse reactions
• They can overcome maternal antibody interference
• They are bivalent if the vector itself is a vaccine strain
• They express only one or two foreign antigens from the pathogen, making it easy to distinguish infected from vaccinated animals
• They can be adjusted to meet evolving disease challenges

Vaxxitek^® - a successful example of a vectored vaccine

The original Vaxxitek^® HVT+IBD, launched by Boehringer Ingelheim Animal Health in 2006, was the first ever HVT-based vectored viral vaccine developed for poultry. The vector used – HVT – is the herpesvirus of turkeys.

“The vectored vaccine is a bioengineering construct. The HVT vector carries the genes of the immunogenic protein of one or more viruses – in this case IBD,” explains Bublot, a pioneer in the development of HVT as an effective viral vector for vaccines against IBD in poultry, with publications as early as 1995.

In 2019, a new form, Vaxxitek^® HVT+IBD+ND, was launched in the US. It is a “trivalent” vaccine, meaning it induces immunity against three diseases, in this case Marek's Disease (MD), Infectious Bursal Disease (IBD) and Newcastle disease (ND). In 2020, a second trivalent form, Vaxxitek^® HVT+IBD+ILT, received marketing authorization in the US. It protects against MD, IBD and Infectious Laryngotracheitis (ILT). These are all highly infectious and commercially disruptive diseases that affect the poultry industry worldwide.

The first Vaxxitek^® HVT+IBD was extremely successful with more than 130 billion doses sold. “Today, the most recent Vaxxitek^® HVT+IBD+ILT is the first poultry vaccine able to protect birds against these three diseases in only one shot,” explains Stéphane Lemière, Head of Global Technical Services Poultry at Boehringer Ingelheim Animal Health. Thus, these innovative new trivalent products provide poultry farmers and vets with solutions that are highly convenient and cost effective. 

Benefits for animals and humans

As the technology develops, it is likely that vectored vaccines will continue to play a significant role in the control of existing and new emerging diseases not just in poultry but other animals too. For example, the Boehringer Ingelheim canarypox vector platform has been extremely successful for the development of vaccines for companion animals including cats, horses and dogs.

However, while the technology has been used widely in veterinary medicine since the 1990s, until recently it was less common in human medicine. “Our long experience with vectored vaccines in veterinary medicine can make a contribution to vaccine innovation for humans and underlines the value of the ‘One Health’ approach,” says Bublot.

There are still many infectious diseases such as AIDS, malaria, and hepatitis C for which there is no vaccine. Conventional vaccine design technology based on live attenuated vaccines or inactivated vaccines has failed so far, whereas vectored vaccines and other vaccine biotechnologies have been tested for these diseases with, for instance, partial success of a canarypox vectored vaccine for AIDS. That is why it is so important to continue developing new vaccine design technologies. Indeed, multivalent vaccine candidates – those that protect against multiple diseases or strains – are likely to be required for complex diseases like malaria and HIV.

United strengths

For poultry farmers and veterinarians, the latest vectored vaccines provide a much-needed solution. “Today, there are more and more vectored vaccines on the market. They provide many benefits to poultry farmers by improving hatchery administration and safety,” shares Jérôme Baudon, Head of Global Strategic Marketing Poultry at Boehringer Ingelheim Animal Health. But this does not mean that there is no role for conventional vaccines in future. Not all vectored vaccines are equal in terms of performance and in some cases classical vaccines are needed in addition to vectored vaccines.

Bublot points out: “Already now and certainly in future, we will need the strengths of both vectored and conventional vaccines to tackle increasingly complex diseases. To be able to serve the well-being of both humans and animals, we also need to continue innovation efforts in developing new approaches to infectious diseases.”