A total of 117 (94%) participants completed all aspects ofthe study. There were no differences in the proportions of recipientsof 200 or 400 mg of the Chlorella-derived dietary supplementor placebo who achieved at least a 4-fold increase inantibodies (proportions for the 3 virus strains ranged from17.9% to 28.2% for the 200-mg group, from 11.1% to 22.2%for the 400-mg group and from 19.0% to 21.4% for theplacebo group; p > 0.05 for all comparisons). Reports of adverseevents were similar for recipients of the supplement andplacebo, except with regard to fatigue, which was reportedmore frequently by recipients of 200 mg of the supplement(18/41 or 44%) than by those who received 400 mg of thesupplement (8/40 or 20%; p = 0.032) or placebo (8/42 or19%; p = 0.019). Recipients of 400 mg of the supplement whowere 55 years of age or younger had significantly higher geometricmean antibody titres against influenza A/New Caledonia21 days after vaccination (p = 0.047) and against B/Yamanashi7 days after vaccination (p = 0.034); the trends werenonsignificant for titres against A/Panama. We also observedsimilar increases for the proportions of subjects with a 2-foldor greater or a 4-fold or greater increase in antibodies.