Whole-cell pertussis vaccine (DTwP) has no influence on allergic diseases and atopic sensitization in children

Introduction

Immunization has an essential impact on public health worldwide. Numerous studies have shown the efficacy of different vaccines to protect children and adults from various infectious diseases. However, some parents choose not to vaccinate their children for different reasons, such as doubts regarding their usefulness, philosophical or religious opinions and concerns over vaccine safety and efficacy [1]. Parents of children at a high risk of atopy are frequently concerned about the effect of immunizations in infancy. Apart from concerns about rare allergic reactions to the vaccine antigens or contaminants themselves, there exists a fear that immunizations may promote the development of allergic disease [2]. In addition, the rising prevalence of atopic disease today has been attributed to an introduction of the increasing number of recommended vaccines in immunization programs. The concern of vaccine opponents is that the infant’s immune system is inadequately developed to handle vaccines safely or that multiple vaccines may overwhelm the immune system leading, among other things, to higher atopy sensitization and allergic diseases [3, 4]. In routinely recommended vaccines administered over the past 100 years, the whole cell pertussis vaccine (DTwP) contained the highest number of antigens among the other vaccines, including about 3000 of pertussis antigens. The new, acellular pertussis vaccine (DTaP) consists of no more than 5 antigens (depending on the type of formulation) [5]. In most of the developed countries, the replacement of DTwP with DTaP allowed to significantly decrease the number of vaccine antigens in the recommended programs. Whereas previously recommended programs consisted of more than 3000 antigens, nowadays including more kinds of vaccines, it consists of less than 150 antigens (proteins and polysaccharides) [3]. Poland is the only one country in the European Union where infants are vaccinated with DTwP according to the mandatory immunization program. There is an access to DTaP as an alternative option, payable by infant’s parents. As a result of that strategy, about half of Polish infants are vaccinated with DTwP, and the rest of them with DTaP. That is why the exposure to the number of vaccine antigens varies significantly between those two groups of children.

Aim

The aim of this study was to verify the hypothesis about the association between the vaccine antigen overload derived from DTwP and the subsequent development of atopic sensitization and allergic diseases.

Material and methods

This is a prospective cohort study, combining environmental monitoring and molecular approaches with comprehensive neurodevelopment and health assessments. In the analysis we used data from an earlier established birth cohort of children in Krakow, being part of the ongoing, collaborative study with the Columbia University in New York, on the vulnerability of fetus and child to environmental factors. This cohort was described in more detail in the previous publications [6, 7].
Briefly, the enrollment (3 November 2000 – 22 August 2003) included only non-smoking women, aged 18–35 years, with singleton pregnancy, without illicit drug use and HIV infection, free from chronic diseases such as diabetes or hypertension and residing in Krakow for at least one year prior to pregnancy. Children were followed up to the 6th year of life. Each year, mother or father were asked to provide information on infants’ health and household characteristics to trained interviewers, who carried out detailed, face-to-face standardized interviews. Information on parental atopy was also collected.

Vaccination data

The data on infants’ vaccination history (date of vaccination and type of vaccine) were extracted from the physician’s records when the children were 3 years old. The status of vaccine antigen exposure was based on different types of vaccines against pertussis (DTwP or DTaP) in a primary course (three vaccine doses up to 8 months of life). Children with longer vaccination delays (25%) were excluded from the study. Children’s vaccination status was divided into three groups:
– the vaccination course completed with DTwP included about 3000 pertussis antigens (manufactured in Poland by Biomed Krakow),
– the vaccination course completed with DTaP included up to 5 pertussis antigens (Tripacel Sanofi Pasteur or Infanrix GlaxoSmithKline vaccines),
– the mixed course (DTwP + DTaP).
The exposure to other vaccines was similar in all three groups. Infants have been vaccinated according to the Polish vaccination schedule against hepatitis B and poliomyelitis, usually simultaneously with DTP. All of the used vaccines contained aluminum as an adjuvant.

Atopy

Allergic diseases such as eczema, hay fever and asthma were diagnosed by a physician and reported every half a year from the 1st to 6th year of life by the child’s parent.
All skin prick tests (SPT) were performed when children were 5 years old, using four common aeroallergens: Dermatophagoides pteronyssinus, Dermatophagoides farinae, cat and dog hair. Additionally, in a smaller subsample, sensitization to mold as well as tree and grass pollens was also checked. The standardized extracts of allergens were used, including a positive and negative control solution. The technique of the tests was consistent with standards recommended by the European Academy of Allergy and Clinical Immunology. The tests were performed by trained nurses in one of out-patient allergy clinics. The results were read after 15 min by measuring the largest diameter of the wheal. Sensitization status was interpreted as a positive when a wheal had the diameter of 3 mm and not smaller than the histamine control.

Dosimetry of Pb in blood

Lead concentrations were examined in cord blood (at delivery) and in capillary blood (5-year-old children). Whole blood lead concentrations were determined using inductively coupled plasma mass spectrometry CLIA’88 method “Blood lead cadmium mercury ICPMS_ITB001A”. This multi-element analytical technique is based on quadrupole ICP-MS technology [8]. More details on blood sample collection and analysis were presented in the earlier publications [7, 9].

Statistical analysis

Descriptive statistics were reported in a standard way (number and proportion; mean and/or median, and standard deviation). Exposure to DTP vaccine (see above) was categorized according to its type. Differences in the distribution of women’s and newborns’ parameters grouped by categorized DTP status were tested using 2 or Fisher’s exact test (for nominal variables) and one-way ANOVA or Kruskal-Wallis tests (for continuous variables).
Candidate confounding factors were selected based on the current literature. They include: gender, birth weight (continuous variable), parity, maternal age (continuous variable), education (university vs. non-university), marital status (married vs. unmarried) and poor economical status, maternal or paternal atopy, breastfeeding (child breastfed for at least 6 months), exposure to environmental tobacco smoking (ETS) prenatally and in a 6-year period of life, presence of a dog or a cat at home for at least a month in a 6-year period, indoor environment (presence of damp or mold at home) and blood lead level (cord blood and measurement at the age of 5 years). Maternal and paternal atopy was defined as reported medical diagnosis of eczema, atopic dermatitis, hay fever or food allergy.
The candidate factors were first evaluated together with the type of DTP vaccination and were retained in further analyses only if they were statistically significant in a consistent way or influenced the course of DTP vaccination. In subsequent multivariable analyses, the set of confounding factors was further optimized, separately for each outcome. Associations were measured by multiple logistic regressions. Odds ratios were estimated either without any other factor than exposure (crude OR) or with the confounding factors (adjusted OR). Statistical analyses were performed using SPSS 22.0 software.

Ethical approval

The parents of all children involved in the study gave their informed consent. The research protocol was approved by the Jagiellonian University Ethical Committee.

Results

The analyzed population consisted of 234 children: 53.4% – boys and 46.6% – girls. Infants up to the age of 8 months were vaccinated with a primary course against pertussis, with DTwP – 60.7%, DTaP – 32.9% and further 6.4% with the mixed course (DTwP + DTaP).
As for study group characteristics, only maternal education, poor economical status, mother’s atopy and ETS exposure significantly differed in the primary course of DTP vaccination. Mothers who graduated from university more often vaccinated their children with DTaP (63.6%) and infants of mothers with atopy were more likely to be vaccinated with the mixed course (40.0%). Infants prenatally exposed to ETS have been significantly more often vaccinated with DTwP in the primary course (45.1%) (Table 1). All of those confounders were included in multivariable analysis.
The frequency of allergic diseases and assessed sensitivity for the selected allergens did not differ significantly between groups exposed to DTP in children at the age of 6 years. Hence, the cumulative incidence of asthma, eczema and hay fever from the 1st to the 6th year of life was similar in the three pertussis vaccination groups (Table 2).
Our univariate analysis showed that only the exposure to DTwP vs. DTaP was associated with a decreased risk of developing eczema in children (calculated for cumulative incidence), (OR = 0.55; 95% CI: 0.31–0.99). There were no significant relationships between any of vaccination groups and allergic disease and allergen sensitivity in the multiple logistic regression model with adjustment for maternal education, poor economical status, mother’s atopy, prenatal ETS, parity, breastfeeding, dwelling in damp or moldy conditions (Table 3).

Discussion

In the present study, children vaccinated with DTwP were at a similar risk of atopic disorders as children vaccinated with DTaP. The burden of about 3000 antigens derived from DTwP on the infants’ immune system in comparison to 4 antigens included in DTaP had no influence on the development of allergic disease and atopic sensitization in children up to the 6th year of life.
Our results did not confirm that the theoretical issues, raised by many vaccination opponents, such as immune “overload” by a great number of vaccine antigens in infancy is linked with a higher risk of allergy in children [10]. We obtained the consistent results for all of the analyzed allergic diseases (eczema, hay fever, asthma), and performed tests for allergen skin sensitization. In the previous studies, there was inconsistent evidence for a relation between vaccination and the development of allergic disease. Usually most of the children are vaccinated and it is difficult to obtain adequate numbers of unvaccinated infants to examine the vaccination-allergic disease relationship. Hence, unvaccinated children are a highly selected and usually atypical group. It is related to studies on DTwP as well [11–14].
In our cohort, only 5 infants have not received routine vaccination and we excluded them from the study group to avoid the bias of medical and socio-economical confounders related to refraining from vaccination. Therefore, we decided to calculate the relationship between the heavy burden of vaccine antigens derived from DTwP (about 3000 antigens) in comparison to the exposure to DTaP which included up to 5 antigens. That difference in the burden of vaccine antigens was sufficiently significant to conduct our analysis. The rest of vaccine exposure was similar in the two study groups. We realize that the time of vaccination exposure is important in our analysis and that period was limited up to the 8th month of life. Infants with a longer delay in primary DTP vaccination course have been excluded from the study cohort. The relatively short period of vaccination exposure and including in the analysis only the vaccinated children decreased the bias of reverse causation. The onset of allergic disease usually occurred after the vaccination exposure, and any earlier potential symptoms of allergy did not influence the immunization procedures because the entire cohort was vaccinated against pertussis. The crucial reasons for the vaccine choice (DTwP or DTaP) for infants were dependent on socio-economical factors which were included in the analysis as the important confounders.
The previous studies about the relationship between DTwP exposure and allergy had compared vaccinated groups with the unvaccinated one. The studies conducted that way yielded inconsistent results. Our results are consistent with the observations of other authors who did not confirm the influence of DTwP exposure on the development of allergy [11, 15, 16]. Some of them even observed the protective effect of DTwP vaccination with respect to the onset of asthma and other allergic diseases in later life [17–19]. On the other hand, some other reports indicated the adverse effects of DTwP vaccination on the development of allergy [12, 20, 21]. That fact may result from the methodological differences in the epidemiological studies and the ascertainment bias linked with refraining from vaccination as well as the lack of data about the important confounders. The advantage of our study is its design – the prospective cohort study with reliable data on vaccination exposure, allergic disease onset and skin prick test results. We had a possibility to adjust the crude results to many plausible confounders that could influence the development of allergy in early childhood. The advantage of our study is the active, long-term (9-year) survey of the study cohort. In this paper we decided to present the results of a 6-year survey, when children were administered with skin prick tests. The available data on allergic disease onset in children up to the 9th year of life gave us the possibility to calculate the same analysis for older children, as well. We obtained similar results like for the younger children – no relationship between DTwP exposure and the development of allergy.
We realize that study on DTwP seems not so important for the most of the developed countries because they removed that vaccine from their vaccination programs. Poland is the only country in the EU which still uses DTwP in its mandatory vaccination schedule. DTwP is relatively responsible for most of the adverse effects following immunization (AEFI) reported in Poland. Knowing the numbers of AEFI (observed up to 4 weeks after exposure), the Polish community is concerned about the long-term vaccine influence on children’s health. On the other hand, still using DTwP we had the possibility to test the hypothesis popular in the other countries of the “overload” of the immune system with vaccine antigens with respect to the development of allergy. DTwP exposure affects the infant’s immune system with 10 times more antigens compared to the entire spectrum of other vaccines applied nowadays in vaccination programs of the developed countries [3]. Lack of the effects of DTwP exposure on the development of allergy indirectly indicate that the cumulative number of antigens derived from the increasing number of new-generation vaccines, including usually only a few antigens, has no harmful influence manifested by an increased risk allergic diseases in children.

Conclusions

The exposure to a large number of vaccine antigens derived from DTwP has no influence on the development of allergic disease and atopic sensitization in children. The results of our study should not be treated as a supportive argument for the continuation of using DTwP which is responsible for too many AEFI in infants. They are further evidence on the vaccines safety which should encourage parents not to avoid or delay effective immunization of children, especially when weighed against the benefits.

Acknowledgments

The authors would like to thank all co-workers from the Chair of Epidemiology and Preventive Medicine, Jagiellonian University Medical College for their help in collecting the data.
All the studied children were a sample from a cohort study on the susceptibility of fetus and child to environmental factors, followed in Krakow with the Columbia University in New York.
The study received funding from NIEHS R01 grants entitled: “Vulnerability of the Fetus/Infant to PAH, PM2.5 and ETS” and “Developmental effects of early-life exposure to airborne PAH” (R01ES010165 and R01ES015282) and from The Lundin Foundation, The John and Wendy Neu Family Foundation, and The Gladys and Roland Harriman Foundation. Principal investigator: Professor FP Perera; co-investigator: Professor W Jedrychowski. NIEHS, the Lundin Foundation, the Gladys T. and Roland Harriman Foundation had no role in the design, analysis or writing of this article.

Conflict of interest

The authors declare no conflict of interest.

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