This is a relevant study I found on quinine’s antiviral activity (albeit on a different virus):
A previous study reported that the
antimalarial drug chloroquine, a drug that shares a similar chemical
property with quinine (both are alkaline in nature), inhibits pH-dependent
stages of Flavivirus replication (Randolph et al., 1990). This is a
likely inhibitory mechanism of quinine in our experimental model.
This is a relevant study I found on quinine’s antiviral activity (albeit on a different virus):