RESUMEN
<p><b>OBJECTIVE</b>To investigate the efficacy of a herbal formula in the prevention of influenza or influenza-like syndrome among elderies residing in old-people's home in Hong Kong. The secondary objectives are to investigate the quality of life (QOL) and symptomology changes among the herbal users and to evaluate the safety of this formula.</p><p><b>METHODS</b>In ten old people's home or community centres in New Territories, Hong Kong, 740 eligible subjects agreed to join the study and were randomized to receive a herbal formula or a placebo on alternate days over 8 weeks. Among those 740 participants, 113 had provided blood samples for immunological assessments before and after the study drug. Assessments were done at 0, 4, 8 and 12 weeks. Participants were instructed to keep a daily record of body temperature and any symptoms as sore throat, myalgia, running nose or cough, and to report to assessor accordingly. Those reporting body temperature of 37.8 °C and above would be visited and a proper nasopharyngeal swab be taken for viral study.</p><p><b>RESULTS</b>Seventy-two participants developed influenza-like-symptoms but none of them was proven influenza in their nasopharyngeal swabs, 40 of these patients belonged to the herbal group and 32 to the placebo group, without significant differences between groups. The difference on the changes in QOL between the two groups was not statistically significant. However, in the immunological study, the natural killer cell absolute count was significantly increased in the herbal group compared with the placebo group (463 ± 253 vs 413 ± 198, P<0.05).</p><p><b>CONCLUSIONS</b>The herbal preparation was not effective compared with placebo in the prevention of influenza-like syndrome. It was however safe and possibly supporting immunological responses.</p>