Childhood asthma and allergy: the role of vaccinations and other early life events
Year: 2005
Type: dissertation
Study design: Observational Study
Abstract: Atopic disorders have become increasingly prevalent in the western world during the last decades of the 20th century. Research concerning the cause(s) of this increase has so far suggested a complex interplay between genetic and environmental factors. These studies have also indicated that priming starts at a very young age, even before birth. Therefore most studies on this subject have been in children. No clear causes of the increase of these disorders have come up so far, although there are indications that the increased hygienic living-conditions could play a role. Knowledge of causal factors would open opportunities for prevention. The aim of this thesis was to contribute a small piece to the immense endeavour of building foundations for prevention strategies. It also aimed at yielding objective information on implications of childhood vaccinations as a tool for workers in the field of preventive health care and for the general public. \nThe study population described in the chapters 2 and 4 were 8-12 year old children of the Orthodox Reformed (Protestant) population, living in an area in the Netherlands which stretches from the south-west to the east (study population I). Chapters 3, 5 and 6 apply to retrospectively collected health report data of a cohort of 700 families with index children born in 1988-1990 (study population II). These files contained reports of health check-ups of children living in Zwijndrecht, a town south of Rotterdam, at the age of 6 years. Chapter 1 gives an introduction and discusses the background of the thesis: the prevalence of atopic disorders has increased dramatically in the western world over the last decades of the past century and much effort has been put into finding the cause(s) of this increase. The hygiene hypothesis assumes that this increase is caused by a too hygienic environment where children are not enough exposed to pathogens. This exposure is said to be necessary for a healthy development of their immune system. Extensive research has been conducted to test the hygiene hypothesis, and, although much of the evidence is conflicting, there is some evidence that some aspects of hygiene are related to the development of atopic disorders. In this thesis we focused on two aspects of “hygiene”: vaccinations and family size. Chapter 2 presents a study of the relationship between the diphtheria-tetanus-pertussis-poliomyelitis vaccination (DTPPo) in the first year of life and reported atopic disorders at age 8-12 years. We conducted this study in children of Orthodox Reformed (Protestant) families in the Netherlands (study population I). A part of these families refuse vaccinations for religious reasons, and therefore we could compare vaccinated and unvaccinated children in a rather homogenous population. We included children via Orthodox Reformed schools, sent in total almost 4500 questionnaires of which 1875 (42%) were returned. The conclusion of this study is, that vaccinated and unvaccinated children have an equal risk of atopy. In Chapter 3 we addressed the same research question as in chapter 2. However, this study was conducted in children of 700 families with index children born in 1988-1990 (study population II) and the outcome of interest was atopy at age 6 years. Data were collected from reports of routinely conducted health examinations at the age of 6 years. Although we focussed on the pertussis vaccination at first, it became evident that there was almost 100% overlap with the DTPPo vaccination. The conclusion of this study is, that unvaccinated children had a higher risk of atopy at age 6 years. However, the number of unvaccinated children in this study was small and therefore the result is not reliable on its own. Chapter 4 describes a study on the relationship between the Haemophilus influenzae type b vaccination (Hib) and reported atopic disorders at age 8-12 years. This study was conducted in the DTPPo vaccinated part of study population \nI. The Hib vaccination was introduced in the Netherlands in 1993, implying that a part of these DTPPo vaccinated children did not regularly get the Hib vaccination in the first year of life. This study concluded that there was no indication for a different risk of atopy due to the Hib vaccination. In Chapter 5 we investigated the so-called “sibling effect” (the phenomenon first described in 1986 that children from larger families have a smaller risk of atopic disorders than children from small families). This study was conducted in study population II. Because we studied the sibling effect within families, we were able to disentangle the independent effects of sibship size and birth order. In an ordinary cohort of children these variables are usually strongly correlated and it is consequently not possible to disentangle their effects From this study it became evident, that a higher birth order (or a higher number of older siblings) is associated with a lower risk of allergy, independent of the size of the sibship. In chapter 6 we studied the associations of atopy at age 6 years with perinatal characteristics (gestational age, birth weight and neonatal head circumference) and obstetric complications. These associations were studied in population II. We concluded, confirming earlier findings, that premature children have a higher risk of asthma at age 6 years. Other findings were that children with a high ratio of head circumference to birth weight, children delivered with vacuum extraction, and children delivered after induced labour had a higher risk of allergy. \nChapter 7 discusses the findings in this thesis, also in relation to what was already known on the etiology of atopic disorders. \nThe finding that the DTPPo vaccination and the Hib vaccination are not related to atopic disorders is reassuring for those parents who are hesitating about the health effects of vaccinations and could, if communicated well, contribute to stop the, in some countries (like the UK and the Netherlands), steady decrease of the vaccination coverage. \nThe findings on birth order and perinatal risk factors are mere links in a chain of hypotheses on the mechanisms underlying atopic disorders and could thus contribute to preventive strategies in the future. \nWe finally speculate on possible mechanisms on the basis of our findings and results of studies conducted on other topics and make recommendations for daily practice and future research.
Author: R. M. D. Bernsen
Language: English
Subfield: Pulmonary and Respiratory Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2127628450