Stability of closed and needle-punctured vials of Porvac® subunit vaccine against classical swine fever subjected to thermal stress

Classical Swine Fever (CSF) is still one of the most economically important viral diseases of pigs. In endemic countries, the disease is controlled mostly through vaccination; hence, the availability of safe and effective vaccines is of utmost importance. Vaccines intended for application in developing countries must also be thermally stable, since the infrastructure needed to maintain a cold chain in those countries is usually lacking. Porvac is a second-generation subunit marker vaccine against CSF that has demonstrates to be safe and protective. Previous studies have also shown that the vaccine is stable for 1 week at 37 C and have a shelf life of at least 36 months at 2-8 C. The aim of this work was to further explore the accelerated stability of Porvac by assessing the physicochemical properties of the emulsion, and the safety and immunogenicity of the vaccine subjected to more drastic conditions of thermal stress: (1) 25 C for 12 months; (2) 30 C and 37 C for one month and (3) 15 days at 37 °C after the cap of the vials had been needle-punctured. The vaccine subjected to all these conditions did not show significant changes in the physicochemical properties of the emulsion; did not produce local or systemic adverse reactions in pigs, and the chromatographic profile of the recovered antigen was preserved. All vaccinated swine developed neutralizing antibody titers ≥ 1:1000 at 28 days post vaccination. Porvac is stable in all the experimental conditions tested, even after cap puncture, and retains the capacity to induce high titers of neutralizing antibodies, well above the threshold of protection. These results reinforce the robustness of the vaccine, and support its use as a very attractive alternative to modified live vaccines in developing countries endemic for CSF.