Seventeen studies were included (n=85,593 participants, range 121 to 38,808): one RCT (n=121), seven cohort studies (six retrospective and one prospective, n=53,305), two case-control studies (n=14,768) and seven cross-sectional studies (n=17,399). Overall study quality was weak: eight studies were rated as moderate quality and nine as low quality. Not all studies included analysable data.
Vaccination was associated with a significantly higher risk of sensitisation than non-vaccination, when measured by specific IgE level (OR 1.31, 95% CI 1.07 to 1.60, I2=0%; five studies). Sensitisation rates did not differ significantly when measured by skin prick tests (five studies, I2=57%). There was no significant difference between vaccinated and non-vaccinated participants in rates of eczema or atopic dermatitis (nine studies, I2=89%), rhinoconjunctivitis (nine studies, I2=67%), atopic allergic disease (two studies), urticaria (one study) and food allergy (two studies). Vaccination was associated with a significantly lower risk of asthma than non-vaccination (OR 0.73, 95% CI 0.56 to 0.95, I2=91%; 12 studies).
There was substantial heterogeneity for several outcomes. Results of subgroup and sensitivity analyses were reported in the review. Funnel plots showed evidence of publication bias in the analyses of asthma, eczema/atopic dermatitis and rhinoconjunctivitis, but not for other outcomes.