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28th July 2021
According to the World Allergy Organisation, the allergy prevalence among the whole population ranges from 10 to 40%. Moreover, the number people in the UK with allergies, appears to be increasing by 5% every year. One possible cause of the increased prevalence of allergic disease is childhood vaccination although the available evidence is inconsistent. Nevertheless, any perception that childhood vaccination might increase the risk for the development of allergic diseases jeopardises the attainment of herd immunity and the attendant risk of outbreaks of the particular vaccine-controlled infection disease. With gaps in the current evidence, a team from the Faculty of Medicine, Department of Community Medicine, University of Peradeniya, Kandy, Sri Lanka, decided to undertake a systemic review and meta-analysis to examine the relationship between childhood vaccination and allergy. The team performed a search of the main databases such as PubMed and EMBASE for original studies examining exposure (in this case childhood vaccination) and allergic outcome. They restricted the review to randomised controlled trials and prospective cohort studies although did not exclude any studies where there were differences in the timing, number of doses or if the comparators were placebo, controlled vaccine or even no vaccine. The exposure of interest was defined as any childhood vaccination and the primary outcomes of interest were asthma/wheeze, rhino conjunctivitis, allergic rhinitis, atopic eczema, food allergy and allergic sensitisation.
A total of 42 eligible studies were included in the analysis covering vaccination with BCG, pertussis, MMR and DTP. This comprised 35 cohort studies and 7 randomised controlled trials. In their analysis, the authors found that none of the randomised trials found any evidence of an association between BCG or pertussis and allergic manifestations. In fact, two randomised trials observed a reduction in the risk of developing eczema (Risk ratio, RR = 0.83, 95% CI 0.73–0.93) but not for food allergy or asthma. Among cohort studies, childhood vaccination against measles was also associated with a reduced risk of eczema (RR = 0.65, 95% CI 0.47–0.90), asthma (RR = 0.78) and a non-significant reduction in allergic sensitisation (RR = 0.78, 95% CI 0.61–1.01). There was a trend towards a protective effect of measles vaccination against asthma (RR = 0.97), eczema (RR = 0.70) but a slight increased risk for allergy, though none of these associations were statistically significant.
In discussing their findings, the authors noted that there was no clear evidence that childhood vaccination was associated with an increased risk of allergic disease for the commonly given immunisations. In fact, if anything, the opposite was true, with the data suggesting a small, but potentially protective role against the development of eczema, particularly for measles. They concluded that while more studies are required to confirm these findings, it was important to promote the continuation of childhood vaccination to prevent the development of vaccine-preventable disease.
Navaratna S et al. Childhood vaccination and allergy: A systematic review and meta-analysis. Allergy 2021