The adoption of waterinoil (W/O) emulsion vaccines has been central to disease prevention strategies in modern aquaculture. To further improve fish welfare, growth performance, and operational efficiency, PHARMAQ introduced the microdose vaccination concept, reducing the injectable volume from 0.1 mL to 0.05 mL while maintaining high efficacy. The development and implementation of microdose vaccines place stringent requirements on antigen production, formulation robustness, and vaccination accuracy, particularly when multiple vaccines are administered simultaneously by coinjection.
Coinjection, defined as the simultaneous administration of two or more vaccines through a single needle, has become common practice in salmon aquaculture and allows high flexibility in vaccine combinations while limiting the fish to a single puncture. However, this approach introduces additional technical challenges, including vaccine compatibility and the need for highly accurate and precise delivery of each individual dose component.
This contribution provides an overview of formulation aspects of PHARMAQ microdose W/O emulsion vaccines, administration principles, and coinjection strategies used in commercial salmon vaccination. Particular emphasis is placed on the evaluation of vaccination equipment performance. Accuracy and precision of dosing were assessed using established gravimetric methods for singlechannel injection. For coinjection, where conventional weighing cannot discriminate between individual vaccine volumes, a fluorescencebased analytical method was developed. Model vaccines with flow properties matching commercial microdose emulsions were formulated, enabling quantification of the individual contribution of each vaccine within a single coinjected dose.
Using this approach, commercially available vaccination equipment from multiple manufacturers was evaluated. The results demonstrate high accuracy and precision for both single injection and coinjection, with individual vaccine volumes consistently delivered within narrow acceptance limits. These findings confirm that, when combined with robust formulation development and validated administration systems, microdose coinjection can be implemented reliably under commercial conditions.
Overall, this work highlights the importance of integrating vaccine formulation, dosing technology, and analytical methodology to ensure consistent performance of microdose emulsion vaccines in modern aquaculture vaccination practices.