How do we go about imbalanced data for prediction problem?
In addition to post linked by @Wes: 


You should to check other metrics                than accuracy like
precision, recall (especially), F1 score or similar. 
After a certain threshold (lower than the one provided in your
example definitely), it might be worthwile to use anomaly detection
and use your lesser present classes as such.


I would advise against downsampling as it's leaving informations about data, and IMO you would usually want to avoid that.