Researchers at the Hebrew University-Hadassah Medical School in Israel conducted a clinical trial with an elderberry extract to determine its role on influenza severity. Their data revealed higher mean hemagglutinin inhibition (HI) titers to influenza B in the group treated with the elderberry extract than in the control group. A significant improvement of the symptoms, including fever, was seen in 93.3% of the cases in the elderberry-treated group within 2 days, whereas 91.7% of the patients in the control group showed an improvement within 6 days. This suggests that the elderberry extract lessens influenza severity and quickens recovery.

Zakay-Rones, Z., Varsano, N., Zlotnik, M., Manor, O., Regev., L., Schlesinger, M., Mumcuoglu, M. 1995. Inhibition of several strains of influenza virus in vitro and reduction of symptoms by an elderberry extract (Sambucas nigra L.) during an outbreak of influenza B Panama. J. Alt. Comp. Med. 1(4): 361-369.

One possible agent involved in the anti-viral qualities of elderberry was investigated by researchers at the Department of Biochemistry and Molecular Biology in Valladolid, Spain. The researchers isolated ribosome-inactivating proteins (RIPs) in elderberries. To date, the biological role played by RIPs is unknown, however they are hypothesized to serve as anti-viral agents since they inhibit in vitro viral infection. RIPs act as anti-HIV-1 agents through a mechanism which may involve an inhibitory action against the viral integrase. Additionally, RIPs are increasingly being used as the toxic moieties of immunotoxins in experimental cancer therapy due to the ability of RIPs to inhibit protein synthesis.

De Benito, F.M., Iglesias, R., Ferreras, J.M., Citores, L., Camafeita, E., Mendez, E., Girbes, T. 1998. Constitutive and inducible type 1 ribosome-inactivating proteins (RIP) in elderberry (Sambucus nigra). FEBS Letter. 428: 75-79).

The influenza virus is highly contagious in human populations around the world and results in approximately 250,000-500,000 deaths annually. Vaccines and antiviral drugs are commonly used to protect susceptible individuals. However, the antigenic mismatch of vaccines and the emergence of resistant strains against the currently available antiviral drugs have generated an urgent necessity to develop a novel broad-spectrum anti-influenza agent. In a 2013 study, chokeberry possessed in vitro and in vivo efficacy against different subtypes of influenza viruses including an oseltamivir-resistant strain. These anti-influenza properties of chokeberry were attributed to two constituents, ellagic acid and myricetin. In an in vivo therapeutic mouse model, chokeberry, ellagic acid, and myricetin protected mice against lethal challenge. Based on these results, the researchers suggested that chokeberry is a valuable source for antiviral agents and that ellagic acid and myricetin have potential as influenza therapeutics.

Park, S., Kim, J.I., Lee, I., Lee, S., Hwang, M.W., Bae, J.Y., Heo, J., Kim, D., Han, SZ, Park MS. 2013. Aronia melanocarpa and its components demonstrate antiviral activity against influenza viruses.