A 2011 study published in Bio Med Central (BMC) demonstrated that Black Elderberry inhibits the replication of both influenza A and B viruses, as well as three Gram-positive bacteria and one Gram-negative bacteria, which cause upper respiratory infections. 
Researchers at the Department of Virology at Hebrew University-Hadassah Medical School, concluded that the berries are very efficacious as a flu treatment:
“Symptoms were relieved on average 4 days earlier and use of rescue medication was significantly less in those receiving elderberry extract compared with placebo. Elderberry extract seems to offer an efficient, safe and cost-effective treatment for influenza.” 
Hadassah University researchers discovered that the berries confer protection at the cellular level by inhibiting damaging inflammation and enhancing immune system response. They also confirmed that Elderberry is a safe and effective general health tonic.
Read more at thescienceofeating.com