Proper vaccine handling, dosage and administration are key to ensuring thorough and effective coverage. That statement is particularly true when talking about recombinant vector vaccines.
“We have seen in the last 15 years or so that we can have more and more recombinant products protecting birds against multiple pathogens in a single injection,” Guillermo Zavala, DVM, PhD, Avian Health International, told Poultry Health Today. “They are not the solution for everything, but they are certainly very helpful for our goals in the poultry industry, whether you produce meat-type chickens or commercial table eggs.”
However, it’s important not to administer more than one vector vaccine at the same time in the same birds because the vaccines will compete against each other, Zavala noted. This is often the first mistake that people make.
A few other mistakes that can sabotage vaccine effectiveness involve inadequate transport and storage conditions, as well as improper reconstitution and application methods. Related to people, vaccination audits, training and supervision are all important steps to ensure success. Also, motivating employees to apply and maintain good standard operating procedures is necessary, he added.
Don’t cut the dosage
Administering the correct dosage is important for all vaccines, but it’s even more so for recombinant vaccines. “The minute you start fractionating doses in a recombinant vaccine, you are really fractionating the potential protection that you can achieve for the inserts,” Zavala said.
The insert itself is not the issue, he explained. It could be Newcastle disease virus protection, infectious bursal disease virus proteins or avian influenza, “but whatever the insert is, you can easily compromise the potential protection that you normally would achieve,” he added.
That result occurs in two basic ways. “One, if you fractionate the dose, you’re fractionating protection against clinical signs and mortality,” Zavala said. “You’re also fractionating protection against virus shedding.”
If a recombinant-vaccinated flock is infected in the field with a particular disease agent, that flock will shed significantly more virus if the dose was fractionated, Zavala said. “That’s important when thinking about what kind of actions we can implement to limit the perpetuation of disease in the field.”
Vaccine administration options
Recombinant-vector vaccines can be given at day of age or in ovo, but the best method is the one that the vaccination crew is familiar and comfortable with, to minimize mistakes.
The most common method is day of age, delivered subcutaneously underneath the skinfold at the back of the neck. Zalava noted that some hatcheries in Central and North Central Europe use the intramuscular route, where the vaccine is administered directly into the thigh of pullets or baby chicks, which also works.
The in ovo option can achieve more uniform, repeatable results, Zalava said, because it removes people from the equation. As long as the machines are calibrated, disinfected properly, prepped ahead of the vaccination process and the overall area is sanitized, in ovo works very well.
“No system is perfect, but what you’re aiming for is close to 100% proper vaccination,” he said.
This option also prepares birds for potential virus infection in the field. “They have the vaccine virus circulating in their blood before they get challenged; the consequences will not be as severe,” Zavala said.
Other steps toward success
Other factors that influence vaccine effectiveness should be part of the overall program as well. First on Zavala’s list are actions that dilute disease agents circulating in the field.
“We cannot sterilize the environment. But we can clean and disinfect [facilities] and apply a proper downtime,” he noted.
His next step is to delay a potential virus challenge. “We know that for many diseases it is very important to delay infection, because the age of highest susceptibility for some diseases is in very young chickens.”
The third factor is to select the right kind of vaccine, with the right virus strain to protect against the specific disease agent.
Taken together, these actions ⸺ properly storing, handling and administrating vaccines, along with biosecurity, sanitation and management ⸺ maximize bird performance and meet animal-welfare and food-safety standards.
Since their introduction (around 2006), recombinant vaccines have grown in number and impact, Zavala said. “Recombinant vaccines are not going to eliminate the need to vaccinate birds in the field, but they can reduce the dependency of using more vaccines in the field.”