Vaccines are essential tools for the prevention and control of infectious diseases in animals. One of the most important steps in vaccine development is the selection of an appropriate adjuvant. The role of the adjuvant in vaccines can be divided into four: improving the immunogenicity of antigens, reducing the amount of antigen, increasing vaccine efficacy, and optimizing antigen uptake . Overall, adjuvants are used to improve vaccine efficacy by increasing the magnitude of the adaptive immune response.
The present study aimed to perform a physicochemical analysis of emulsions evaluating viscosity, density, pH, centrifugation stability, water content and microscopic analysis of four tilapia vaccines that have in common the effect of providing protection against Streptococcus agalactiae serotype Ib. The tests were performed at the Pharmacontrol Quality Control Laboratory Ltda , following the Brazilian Pharmacopoeia (6th edition) and the Cosmetic Product Stability Guide – Anvisa. The main vaccines available on the Brazilian market were evaluated and named as follows: AQUAVAC® Strep Sa-Si, Vaccine A, Vaccine B and Vaccine C.
AQUAVAC Strep Sa-Si uses a water-in-oil (W/O) emulsion that provides a gradual release of the antigen, resulting in a prolonged and more effective immune response. Vaccines A and B feature an oil-in-water (O/W) emulsion, which, despite being easier to inject due to its lower viscosity, results in a shorter-lasting immune response. Vaccine C (W/O) , despite having a high viscosity, has a lower water content, which can compromise the stability of the antigen. The pH parameters show that AQUAVAC Strep Sa-Si (6.76) is close to the ideal pH of 7.2, reducing the risk to fish welfare at the time of application. While Vaccine B (5.57) and Vaccine C (6.29), which have a more acidic pH, can generate greater stress in the animal during vaccination.
The optical microscopy evaluation (500x) shows the vaccine emulsion, where evident oil droplets in a non-homogeneous medium can be observed in the samples of Vaccines A, B and C, even more evident in Vaccine C with an excess in relation to the others. The AQUAVAC Strep Sa-Si v accine emulsion does not present these type of structures , evidencing an overall better homogeneity.
We can suggest in a comparative analysis that AQUAVAC Strep Sa-Si has a superior formula, possible longevity of the immune response, ease of application and homogeneity. This guarantees a continuous and effective release of antigens.