Common Carp Vaccine: Long-Term Immunity and Virulence Stability

We conducted a study to determine the duration of specific immunity in common carp nine months after vaccination. Our results showed that the level of protection provided by the vaccine was comparable to that observed six weeks post-vaccination. To examine the possibility of virulence returning, we performed several experiments.

Firstly, we passaged the vaccine strain in vitro for over 20 times and analyzed the deletion part of the sequence every five passages. We found no mutations compared to the original passage, indicating the stability of the vaccine strain.

Secondly, we passaged the vaccine strain in vivo. At eight days post-vaccination, when the viral charge reached its peak, we isolated the spleen and heart tissues. We then used homogenized tissue to infect naive fish. However, after three passages, we were unable to isolate the virus. This further supports the conclusion that the vaccine strain is stable in vitro and safe in vivo, with no possibility of the virulence returning.

We intend to publish these findings in a future paper.