It depends on the virus, and the type of vaccine (live attenuated, inactivated etc).

For example The in vitro approaches for quality control of live attenuated sheep pox virus vaccine could be conducted using qPCR and virus titration on tissue culture, as 2.5 log 10 TCID50/ dose is considered satisfactory.

Sir, that would depend on the type of virus you choose for development of a vaccine. Sine different assays are used for detection of vaccine seed (if it is a live virus) or antigens (if it is an inactivated virus), accordingly your in-vitro assays will differ.

Please explain in detail precisely what do you want to know?

As far as my knowledge suggests, there are no such in vitro techniques that can give any idea if the vaccine is potent or not. To check the immunogenicity or potency, you need to immunize your vaccine into the animal, then only you can check the immune response or protection.

If you can elaborate on your question in more detail, there is a possibility to get a different answer.

I hope this can help