A cup of green tea may help prevent or lessen the duration of the flu. In a lab study, published in Antiviral Research, EGCG dramatically inhibited influenza virus replication in cell culture in all the subtypes of influenza virus tested. EGCG appears to suppress viral RNA synthesis by altering the properties of the viral membrane.
Song JM, Lee KH, Seong BL. Antiviral effect of catechins in green tea on influenza virus. Antiviral Res. 2005 Nov;68(2):66-74. Epub 2005 Aug 9.