Step-up Trials: Test Vaccine Reactions With Minimal Risk

Change can be daunting, and it can be uncomfortable. This human reaction to change is present regardless of the scenario, which is why it’s not uncommon to experience anxiety when considering a new vaccine program. But change can also lead to a lot of positive outcomes.

One of the main concerns that arise when a new vaccine is being considered is whether or not it will be a detriment to the bird’s health or the level of disease control that the poultry producer is accustomed to. This concern is especially common when a new Salmonella vaccine program is under consideration, which makes a step-up trial a great way to test a new Salmonella vaccination with minimal risk.

What Is a Step-up Vaccination Trial?

A step-up vaccination trial is a methodical approach to testing a new antigen by providing controlled monitoring of the vaccine reactivity in subsets of the bird population. Elanco has used the step-up trial described below to help evaluate potential reactions to a new vaccine in broiler breeders.

Conducting a Salmonella Step-up Vaccination Trial

When conducting a step-up trial, the first step is to set up a split-house study comparing reactivity and mortality rates between the current vaccine and the new vaccine. In this example, the broiler breeder team accomplished this by testing two bacterins on missed-sex males in one of their pullet houses. At 18 weeks of age, the missed-sex males in the pullet house were sorted into two groups. One group was vaccinated with the current Salmonella bacterin and the other group was given the new Salmonella bacterin. Both vaccines were administered in the inguinal fold of the leg, and the birds were painted two different colors for monitoring.

Fourteen days following the vaccination, both groups of male birds were humanely euthanized. The severity of the reaction in the inguinal fold was analyzed using a standardized vaccine reaction scoring system. In addition to the scoring system, mortality records for both groups of male birds were evaluated to see if any birds died before the end of the trial. Both data sets were used to determine if additional trials with the new bacterin should be conducted. In this trial, the male birds given the new Salmonella bacterin exhibited reactions within normal expectations.

The next step in the trial was to vaccinate a subset of the pullet population. One pullet flock was vaccinated every week over a period of one month.  As each flock received the new Salmonella bacterin, they were monitored and detailed records were kept on mortality trends, feed consumption and the overall health of the flock. The monitoring continued as the vaccinated pullets were moved into the henhouse. As positive results were seen, the use of the new bacterin was introduced or “stepped up” to the remaining flocks.

Benefits of a Step-up Vaccination Trial

One of the biggest benefits of a step-up vaccination trial is risk mitigation. If a poultry producer has lost success with their current Salmonella vaccination program and is looking for a new program, the step-up trial strategy provides a humane and effective approach to testing a new vaccination program in broiler breeders. And because the new bacterin is tested on missed-sex males first, and then gradually tested across a company’s pullet flocks, it instills confidence in the new vaccination program.

A step-up trial also allows the poultry producer to be in the driver’s seat when it comes to deciding whether or not to adopt the new vaccination program. If the trial results are not satisfactory, the company can maintain their current vaccination program or try another new one.

The process combines sound study design with detailed observation and helps poultry producers alleviate some of the anxiety and discomfort that comes with changing a pullet vaccination program.

If you are interested in learning more about a step-up vaccination trial, please contact your Elanco technical consultant.