PURPOSE OF THE STUDY.
Influenza vaccines are produced from embryonated hens' eggs and contain residual, variable amounts of egg protein. This study attempted to better characterize reaction risk in a large population of egg-allergic persons.
Patients with egg allergy were recruited from consulting allergists for the purpose of being vaccinated against pandemic H1N1 influenza virus in the fall of 2009. A minority of them had previously been vaccinated for seasonal influenza without reaction. Egg allergy was defined as a minimum of 1 sign or symptom occurring within 60 minutes of ingesting egg, confirmed by either a positive skin-test result or an egg-specific immunoglobulin E (IgE) level of ≥0.35 kU/L. Also included in this group were persons who had no history of egg protein ingestion but who had both a positive egg skin-test result and positive serology results (specific IgE ≥ 2 kU/L if <2 years of age and ≥7 kU/L if ≥2 years). A control group with egg tolerance was included.
This study involved 2 stages, the first of which was conducted by allergists in the population described above. Because the results suggested minimal risk, an expanded program of vaccination was undertaken for patients who self-reported egg allergy. Vaccine was administered in the study population in a single dose to patients deemed at low risk (mild gastrointestinal/skin reactions) and in 2 doses (10% and 90%) at 30-minute intervals for those deemed at higher risk (asthma or cardiovascular reactions). Patients were observed for 60 minutes after vaccination. After the first stage revealed limited risk of anaphylaxis in the first 900 egg-allergic patients, special clinics began a rapid vaccination program with a mandatory surveillance protocol.
Among 830 patients with confirmed egg allergy, 9% had vaccine administered in divided doses. No patient had an anaphylactic reaction. Nine patients had minor allergic symptoms. The proportion of patients who presented with signs/symptoms compatible with an allergic reaction was similar (3.1%) in the control group and the group of patients with egg allergy. In the second stage of expanded vaccination of 3640 additional patients, 2 were treated with epinephrine, although neither of them fulfilled study criteria for anaphylaxis.
Vaccination of patients with egg allergy with adjuvanted pandemic H1N1 vaccine seems to be safe, and the results of this study are in line with those of previous studies performed with seasonal influenza vaccine. Vaccines in this study had low levels of ovalbumin. Further studies might assess the risk after administering vaccine with the higher ovalbumin levels found in seasonal vaccine.
The authors pointed out that patients with the most severe egg-allergy histories might have avoided vaccination altogether. There is still no published study of this much smaller, highest-risk group. However, these results add to others that indicate that vaccination can safely proceed in most children with egg allergy, particularly with vaccines that now have lower egg content.
- Copyright © 2011 by the American Academy of Pediatrics