The present invention relates to pharmaceutical or veterinary or nutritional compositions of polyherbal extracts useful as anti-viral or immune-supporting agents. Particularly, the present invention of polyherbal composition comprises of extracts of Withania somnifera, Mangifera indica and purified Shilajit. This cost effective immune-supporting agent is ideal for use during the maintenance phase of the treatment, following an initial viral load reduction phase in which it is used as an adjuvant to conventional anti-viral drug therapy. The anti-viral and immune-supporting composition of this invention can perhaps be the sole basis of treatment where affordability is an issue. Additionally, this composition is used for the treatment, prevention or management of immune-supporting system in primates in need, especially humans.