At the peak of the SARS epidemic in Hong Kong, hospital workers were under high risks of contraction of the infection. Herbal preparations had been used historically in China to treat influenza-like diseases. During the SARS outbreak, herbal preparations had been used jointly with standard modern treatment in China. As a means to protect the at-risk hospital workers, an innovative herbal formula was created and consumed by 3160 of them in two weeks. During the two weeks, symptoms and adverse effects were close monitored; 37 of them had their serum checked for immunological responses. The results showed that none of the herb consumers contracted the infection, compared to 0.4% among the non-consumers. Adverse effects had been infrequent and mild. There were hardly any influenza-like symptoms and the quality of life improved. In the group who volunteered to have their immunological state checked, significant boosting effects were found. It was concluded that there might be a good indication for using suitable herbal preparations as a means of preventing influenza-like infection. The mode of preventive effect could be treatment of the infection at its very early stage instead of producing a period of higher immunological ability, as in the case of vaccination.