A Cochrane review [Abstract] 1 included 61 studies with a total of 4 149 subjects; 35 studies (n=4 060) provided data in a form suitable for inclusion in the meta-analyses. The studies included children ranging from 6 months to 18 years of age. The echinacea trials differed in the selection criteria of participants as they used children without a significant health problem and without a history of recurrent acute respiratory tract infections (ARTI). The remainder of the trials included a history of recurrent ARTIs in the inclusion criteria. Forty studies used bacterial products, four studies used herbal extracts (echinacea and garlic), 11 studies used synthetic compounds, five studies used thymic extracts (thymomodulin) and one study used a synthetic interferon. Twenty-two studies had a duration shorter than six months, 33 studies had a duration of six months and only six studies had a duration longer than six months. When compared with placebo, the use of immunostimulants (IS) was shown to reduce acute respiratory tract infections (ARTIs) measured as the total numbers of ARTIs (WMD -1.24, 95% CI -1.54 to -0.94; statistical heterogeneity I2 =94%) and the difference in ARTIs rates (WMD -38.84%, 95% CI -46.37% to -31.31%; statistical heterogeneity I2 =83%). No difference in adverse events was evident between the placebo and IS groups
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment and blinding) and by inconsistency (high level of statistical heterogeneity).
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