The most sought-after commodity in areas hit by the H7N9 flu outbreak is a 10-yuan ($1.60) herbal remedy, indigowoad roots, or banlangen, which has been selling out in stores across Shanghai and Jiangsu, Zhejiang and Anhui provinces.

Daily supplies at pharmacies are being cleared within hours, and demand is so high the government has imposed strict price restrictions to prevent profiteering.

No one is absolutely certain what the humble herb can do to fight the disease, but Jiangsu provincial health bureau said on April 3 that banlangen can keep the H7N9 virus at bay, something which has eluded most advanced medicines, suggested pharmacists.