A possible link between immunization and asthma is of great concern to many parents. As the authors of the paper I discuss today have stated: “It is important that researchers clarify this issue, because… the perception that immunization causes asthma may become a significant determinant of parents’ attitudes toward routine vaccination of their children.”

Fortunately, Dr. Ran Balicer and his colleagues published a systematic literature review of this very subject in the journal Pediatrics in November 2007. Dr. Balicer and his co-authors are with the Department of Epidemiology at Ben-Gurion University of the Negev in Israel. I hope it makes everybody happy that neither Dr. Balicer nor any of his co-authors work for a pharmaceutical company or the CDC, nor did they accept any money from drug companies during their research. The title of their review is, “Is Childhood Vaccination Associated With Asthma? A Meta-Analysis Of Observational Studies.”

The aim of the study was to study the available evidence on the association of whole cell pertussis (whooping cough) and BCG vaccination with the risk of asthma in childhood and adolescence. The major electronic medical databases (Medline, National Library of Medicine Gateway, and Cochrane Library) were searched, and reference lists of publications were reviewed for relevant birth-cohort studies and randomized controlled trials from 1966 to March 2006. 71 original scientific studies were found and read in full.

Studies had to meet the following criteria to be included in the meta-analyses:
(1) Directly compared vaccinated and unvaccinated children.
(2) Validated vaccination status by medical charts.
(3) Used preset criteria to define asthma.

Seven studies of pertussis vaccination (with a total of 186,663 patients) and five studies of BCG vaccination (with a total of 41,479 patients) met the authors’ inclusion criteria. Here are the results in two tables. An odds ratio of 1.00 means that there is no relationship between immunization and asthma.


No statistically significant association was detected between either whole cell pertussis or BCG vaccination and incidence rates of asthma during childhood and adolescence. The authors conclude: “Currently available data…do not support an association, [causal] or protective, between receipt of the BCG or whole cell pertussis vccine and risk of asthma in childhood and adolescence.” These are the two vaccines that have been studied the most in this context. The authors hope, as do I, that “these findings could be used to rellieve parental concerns that could otherwise lead to vaccination refusal.”

As a scientist, I need to add two caveats:

1. This is still not a 100 percent settled issue for two reasons, which Balicer et al. openly acknowledge:
(A) “The multitude of biases in studies that have used a birth-cohort design stress the need for additional adequately controlled, large-scale studies.”
(B) Balicer et al. ranked studies on quality. The pertussis vaccination study that they ranked as the highest quality was the UK Retrospective Study of Farooqi and Hopkin. (Farooqi IS, Hopkin JM. Early childhood infection and atopic disorder. Thorax 1998; 53: 927-32.) This investigation did report a positive association between pertussis immunization and asthma, with an odds ratio of 1.44 (95% CI: 1.17 - 1.85), even though this was the only study that did find such an association.

2. A recent study of children born in Manitoba, Canada in 1995 found that Delay in diphtheria, pertussis, tetanus vaccination is associated with a reduced risk of childhood asthma (McDonald KL, Huq SI, Lix LM, Becker AB, Kozyrskyj AL. J Allergy Clin Immunol. 2008;121: 626-31). However, this was a study of the timing of vaccination among vaccinated children. As the authors of the study admit: “To our knowledge we are the first to report that delay in adminstration of the first dose of DPT immunization is significantly associated with reduced risk of developing asthma in childhood.”

In sum: A recent systematic literature review of high-quality studies that directly compared vaccinated and unvaccinated children, validated vaccination status by medical charts, and used preset criteria to define asthma found no association between childhood vaccination and asthma.

Sphere: Related Content


38 Responses to “Childhood Vaccination Is Not Associated With Asthma”  

  1. 1 Tye

    Hi Epi, just thought I’d point out “significant” is misspelled in the first paragraph. Love to read the blog and keep up the good work getting the important news out!

  2. 2 HolfordWatch

    This is very timely, we are just detailing the anti-vax stance of a popular nutritionist in the UK who tends to distort the research: we have been waiting to deal with his claims relating to asthma because it relies on the Manitoba cohort (McDonald et al, 2008) and ignores the Avon Cohort (Maitra et al, 2004, UK prospective).

    It will be interesting to see if the timing association reported in the Manitoba cohort is confirmed in other studies and if any such association persists with the use of acellular rather than whole-cell pertussis vaccine.

  3. 3 EpiWonk

    @Tye: Thanks. I’ve corrected the typo. And thanks for the post at your blog.

  4. 4 Tye

    No problem, thanks for taking a look. As always I enjoy your perspective on the literature and its significance to public opinion.

  5. 5 Herry Peter

    Well Dr. Balicer had explained very well about the Asthma!! For children it is most common thing,so we have to take care of child’s very carefully form asthma.

  6. 6 Jupiter

    Hi, Epiwonk!
    Really enjoying your blog over here.

    Just a couple of other caveats to add.

    1)There’s also this fairly recent finding (which, of course, needs to be replicated before being taken too seriously)

    http://www.ncbi.nlm.nih.gov/pubmed/18086216?dopt=Abstract

    “There was a positive association between pertussis infection and atopic disorders in the pertussis vaccinated group
    only. From the present study, it cannot be concluded whether this association is causal or due to reverse causation.”

    Which might go along with this:
    http://tinyurl.com/6cf7bj

    “Summary
    The global expression of immune response genes in infants after vaccination and their role in asthma and allergy is
    not clearly understood. Pharmacogenomics is ideally suited to study the involved cellular responses, since the
    expression of thousands of genes can be assessed simultaneously. Here, array technology was used to assess the
    expression kinetics of immune response genes with association to asthma and allergy in peripheral blood mononuclear
    cells (PBMC) of five healthy infants after vaccination with Infanrix-Polio Hib. At 12 h after in vitro
    re-stimulation of the PBMC with pertussis toxin (PT) antigen, 14 immune response pathways, 33 allergy-related and
    66 asthma-related genes were found activated. ”

    2) aluminum adjuvants stimulate an IgE-heavy immune response, so you really need to look at asthma and allergy in
    a cohort who recieved all 4 aluminum adjuvanted vaccines and compare that to those who recieved none.

    Go down to page 114 here to read a bit about aluminum and the potential Th2/IgE “bias” created by that adjuvant:

    http://tinyurl.com/6fdpwb

  7. 7 EpiWonk

    @Jupiter:

    Any replication of the Bernsen et al finding should also try to use medical records to confirm pertussis infection and atopic disease, as per the studies in the Balicer et al meta-analysis above.

    I hesitate to comment on your other observations, since I’d prefer to stick to epidemiology, which is my area of expertise. If anyone else knowledgeable is looking at this post from July 21, let her/him comment.

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