Eight studies were included in the review: three RCTs (508 participants); four CCTs (2,074 participants); and one cohort study (10,028 participants). The overall study quality was described as low, reporting was poor, and there was limited information on how specific adverse events were defined or variability in definition. Three studies (one RCT, one CCT and the cohort study) were excluded from the synthesis; two did not use an adjuvant comparator; the cohort study was described as having inconsistencies. Length of follow-up in the studies ranged from 24 hours after each immunisation to six weeks.
Aluminium hydroxide versus no adjuvant in children up to 18 months old: There was significantly more erythema and induration up to seven days after vaccination containing aluminium hydroxide compared to no adjuvant (OR 1.87, 95% CI 1.57 to 2.24; 2,231 observations), and significantly fewer reactions of all types up to 24 hours after vaccination (OR 0.21, 95% CI 0.15 to 0.28; 975 observations). There were no statistically significant between group differences for the other adverse events.
Aluminium of any type versus no adjuvants in children from 10 to 16 years old: There was significantly more local pain up to 14 days after vaccination containing aluminium compared with no adjuvant (OR 2.95, 95% CI 1.25 to 3.38; 395 observations); this was not statistically significant in the random-effects sensitivity analysis. There were no statistically significant between group differences for the other adverse events.