A practical approach to immunization in atopic children

[MMR vaccine and egg allergy. Experience in a hospital immunization unit]

INTRODUCTION

We review the scientific evidence on the safety of the measles, mumps, and rubella (MMR) vaccine (produced in chicken embryo cell culture) in children with egg allergy. Data on the reactogenicity observed with this vaccine in a large series of children with this type of allergy immunized in an hospital immunization unit are presented.

MATERIAL AND METHODS

An observational prospective study was performed in the International Immunization Unit of the Epidemiology and Preventive Medicine Service of the Vall d'Hebron University Hospital from March 2004 to December 2005. Demographic variables, clinical history of allergy, and the adverse reactions observed 30 minutes after vaccine administration were analyzed.

RESULT

A total of 140 patients (106 referred for the first MMR vaccine dose, and 34 for the second) were evaluated. Of these, 75.7 % showed clinical signs after egg ingestion (severe reactions were described in only seven patients: respiratory distress in six and systemic anaphylaxis in one). The MMR vaccine was administered to 121 children. No significant adverse reactions were observed (17.8 % of the vaccinated children developed mild local symptoms).

CONCLUSIONS

According to current scientific evidence and the data obtained in this study, the MMR vaccine is safe in patients with egg allergy.

The complex link between immunization against childhood diseases and allergy

Vaccines can be at the origin of allergic manifestations in susceptible children. Such manifestations include: immediate-type hypersensitivity (anaphylactic shock, rash or angioedema) within 1 h after the injection; semi-late hypersensitivity (local inflammatory lesion such as the Arthus phenomenon) a few hours after the injection; and delayed-type hypersensitivity (abscess or eczema at the site of the injection). Furthermore, early-life vaccinations have been implicated in the modulation of the immune system as they could promote the development of allergy by avoiding infections. However, most population-based studies have not found an increased risk of allergies in vaccinated children. Due to methodological problems in conducting the studies, further investigations are needed to better understand the phenomenon.

Immunization and atopy: possible implications of ethnicity

The possible effects of immunization on subsequent development of asthma and atopy remains a matter of controversy. Although some studies have suggested that immunization might increase the risk for atopic disease, a number of studies have found no association or have even reported a protective effect for immunization against atopy. Recent studies have provided evidence that ethnicity might affect the susceptibility to the immunomodulatory effects of vaccination. In this review the association between immunization and atopy and the effect of ethnicity on this association are briefly outlined. The focus will be particularly on BCG vaccination.

[Adverse reactions to vaccines]

Adverse reactions to vaccines are highly varied, ranging from mild local reactions to fatal outcomes. In the last few years many adverse reactions have been attributed to vaccines, often without justification. In agreement with the World Health Organization, these reactions can be classified as follows, depending on the cause: vaccination-induced reactions (due to an effect of the vaccine itself or to an idiosyncrasy); reactions due to errors in storage, manipulation and/or administration; and coincidental reactions (no causal relationship with the vaccine). Hypersensitivity reactions fall into six categories, depending on the causative agent: reactions due to some component of the infectious agent or one of its products; reactions due to adjuvants: aluminium hydroxide; reactions due to stabilizers: gelatin; reactions due to preservatives: thiomersal; reactions due to antibiotics: neomycin; and reactions due to a biological culture medium: chicken embryo cells. Allergic children should not be excluded from the normal vaccine calendar. Immunologically, allergic individuals are more susceptible to infection and to microbial and viral diseases, which often play an aggravating role. Rubella, whooping cough, and influenza usually exacerbate respiratory allergies. Non-vaccination carries a marked risk of contracting serious diseases such as poliomyelitis, tetanus, and diphtheria, etc. In a not too distant future, the techniques of genetic recombination and monoclonal antibody production will allow the creation of vaccines from organisms that cannot be cultivated in the laboratory or that produce small quantities of antigen. These techniques will also lead to identification of the antigens with the greatest immunogenic power and, consequently, to extremely pure vaccines. The adverse reactions to vaccines referred to our service account for between 0.59 % and 1.27 % of first visits in the last three years. We recorded a total of 48 adverse reactions to vaccines. Of these, 44 were attributed to the tetanus vaccine (92 %), 2 to the measles-mumps-rubella vaccine (4 %) and 2 to the meningitis A and C vaccine (4 %). Clinical features consisted of urticaria (11 cases), urticaria with angioedema (7 cases), pseudo-shock (5 cases), fever and urticaria (4 cases), local reactions (4 cases), persistent crying with exanthema (3 cases), giant local reactions with angioedema of the limb (3 cases), anaphylaxis (3 cases), fever > 39.5 C (2 cases), bronchospasm (1 case), and severe atopic dermatitis (1 case).A regimen of hyposensitization to tetanus toxoid was required in 20 patients (45 %); in three, this could not be completed due to generalized urticaria but all the patients presented protective titers with diluted vaccine.

[Vaccination in children with egg allergy]

Vaccination of children who are allergic or assumed allergic to eggs still creates concern and complication for both the doctor and the patient. These concerns are based on a 1985 circular which has always been liberally interpreted and not well understood. Further analysis of the circular and a review of recent literature show, that most of the time, no special precautions need to be taken before vaccination of children with egg allergy.