Sunday, August 29, 2010

Giving Influenza Vaccine to Egg-Allergic Patients

From Medscape Pediatrics > Viewpoints

William T. Basco, Jr., MD

Pediatrics. 2010;125:e1024-e1030

Study Summary
In this article, Chung, Huang, and Schneider review the conflicted state of affairs with respect to giving influenza vaccine to patients with egg allergy. Given that many patients with egg allergy also have asthma, which places them at high risk for morbidity from influenza illness, the patients who might benefit most from influenza vaccination have difficulty getting it.

The current approach for administration of influenza vaccine to patients with egg allergy involves 3 steps:
(1) skin prick testing with the vaccine;
(2) administration of a low dose of vaccine; and
(3) administration of the remainder of the vaccine. The sequence is completed only if the patient does not react at each successive stage.

The aim of this study was to determine the safety of skipping the first stage, skin prick testing.
The investigators reviewed the outcomes of patients with egg allergy who were immunized against influenza at 1 institution from the 2002/2003 influenza season to the 2008/2009 season.
The participants were 6 months to 18 years old; all had egg allergy as determined by a series of criteria that included skin test results, RAST test results, and history of clinical allergic reaction to egg.
During the first 5 influenza seasons studied, the institution followed the 3-step protocol of skin testing, followed by administration of 10% of the vaccine dose (followed by 30 minutes of observation), followed by administration of the remaining 90% of the vaccine dose.

During the last 3 seasons evaluated, the investigators eliminated the skin-testing step and gave the influenza vaccine in the graded fashion. The clinical notes included data about both local and systemic reactions (urticaria, wheezing, or exacerbation of eczema). They skin-tested 146 participants before influenza vaccination during the first 5 influenza seasons. Ninety-one (62.3%) had a positive skin-prick test, and 55 had negative skin tests (53 of whom received influenza vaccine). Three subjects with a positive skin-prick test still received the influenza vaccine. Therefore, 56 participants received influenza vaccine under the 3-step protocol compared with 115 who received the vaccine later under the 2-step protocol.

A large majority of participants in both the 3-step group and the 2-step group had allergies to more than 1 food (91% and 84%, respectively) and had atopic dermatitis (71% and 64%, respectively). The groups were slightly different in other ways; specifically, the 3-step group had a higher mean age (6.2 years vs 3.9 years), a higher frequency of asthma (76.8% vs 49.6%), and higher rates of allergic rhinitis. Many of the differences were a result of a change in influenza vaccine recommendations during the study period such that the later period included more patients without asthma and younger children who had egg allergy. The study authors attempted to adjust for these between-group differences by using propensity scores in their regression analyses. No differences were seen in the percentages of participants who tolerated influenza vaccine without any reaction (78.6% in the 3-step group and 79.1% in the 2-step group). The frequency of tolerating vaccine without a systemic reaction was 94.6% and 96.5%, respectively, in the 3-step and 2-step groups. Seven subjects (3 in the 3-step group and 4 in the 2-step group) had systemic adverse reactions, and another 29 experienced localized adverse reactions. None of the participants experienced anaphylaxis. The investigators concluded that the influenza vaccine can be administered safely to patients with egg allergy in a graded approach, without first conducting skin prick testing.

Although propensity scores can eliminate bias, they do not eliminate all bias. It is difficult to know how much the differences between groups might have affected the outcomes, but the raw percentages for adverse reactions are similar despite the differences in the patient populations. The investigators reviewed several advantages of skipping the skin-testing step, including the time required to administer and observe the test, the fact that patients must discontinue antihistamines prior to skin testing, and the fact that false-positive skin-testing results can occur from local irritation reactions. It is also important to remember that none of these subjects had a history of anaphylactic reaction to eggs, so these results should not be extended to that high-risk group.


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