The Soviets captured some 300 German rocket scientists and forced them to work on their space programme. They likely would have acquired more had their reputation not encouraged others to flee West.

There's a range of factors that could create a gulf between detecting a viable virus in the laboratory and a real-world risk of infection. For degradation, the environment is likely to be much more tightly controlled in the laboratory (low UV, reduced airflow, ect.). For exposure, a hand briefly touching a surface is very different from doing an intensive swab. For viability, the virus may be encapsulated in the fomite in such a way that it doesn't release back into the body in a viable form.

The other frustrating aspect to Soviet railways was that Soviet trains were designed for much longer runs between replenishment, due to the vast empty spaces of parts of the USSR. This meant that, even if the supporting infrastructure could be captured, additional resupply stops would have to be added to keep German trains topped off.