H1N1 Vaccine May Be Safe for Those With Egg Allergies

Providers can skip precautionary measures when giving egg-allergic children including those with a previously severe reaction the H1N1 influenza A vaccine, according to a new University of Michigan Health System-led study.

In a controlled study of 19 non-egg allergic patients and 105 egg-allergic pediatric patients, which included 25 with a history of egg-induced anaphylaxis, all received the vaccine without developing an immediate or serious reaction to the primary or booster shots. Anaphylaxis is a severe and potentially life-threatening reaction which may be caused by a food allergy.

There were no differences between those who received the vaccine as a full dose and those who received it in two stages, says Matthew J. Greenhawt, MD, MBA, clinical lecturer at the U-M and the studys lead author.

A preliminary skin test to the vaccine, which was performed for all study participants and used to determine the vaccination method, was found to not be predictive of symptom development or vaccine tolerance. Historically, pre-testing has been used to determine a patients risk of developing symptoms.

Previous clinical studies have shown most egg-allergic individuals can safely receive the egg-containing immunization if providers follow certain precautions, including use of the skin test and a two-step graded dose (10 percent, followed by 90 percent of the age appropriate dose after a brief observation period).

"This offers good evidence that administering H1N1 as a single, full dose without pretesting or graded challenge is safe and well tolerated in any type of egg-allergic patient, including those with prior egg-induced anaphylaxis," says Greenhawt.

Results of the study appear in the November edition of Annals of Allergy, Asthma & Immunology.

The global pandemic of the H1N1 Influenza A virus in 2009-10 led to an urgent need to provide the vaccination, prompting re-evaluations on the safety of administering egg-containing immunizations to egg-allergic children and adults.

In the past, egg-allergic individuals were advised to not get the H1N1 vaccine or seasonal Trivalent Influenza Vaccine (TIV) which are both grown on embryonated chicken eggs out of fear they would trigger an allergic reaction because both contain egg protein.

Participants received their immunization between Oct. 15, 2009, and Feb. 4, 2010, at U-M allergy clinics. A questionnaire was distributed prior to vaccination to gather information on an individuals egg allergy history, such as the age of onset and past seasonal influenza vaccination.

Eighty-three of 124 patients recorded a negative skin test result and received a full vaccine dose, while the 41 who tested positive received a 2-step graded dose.

A history of egg anaphylaxis did not increase the odds of a positive skin test. For example, 12 of the 25 with a history of egg anaphylaxis tested negative compared with 13 who tested positive.

"Although these results are from a relatively small study population, they suggest that it is unnecessary to withhold the vaccine from patients with a history of egg-induced anaphylaxis," says study senior author Georgiana Sanders, MD, MS, clinical assistant professor of internal medicine, and pediatrics and communicable diseases.

Providers asked the 110 children who were younger than 10 years to return at a minimum of 4 weeks later for a booster shot because of recommendations from the Centers for Disease Control and Prevention (CDC). The 99 who returned were given the shot without prior skin testing.

All 124 participants received the vaccine without developing an immediate or serious reaction to the primary or booster shots. Researchers reported post-vaccination symptoms, excluding flulike illness, in equal frequency in both those with and without egg allergies.

Last month, Greenhawt and study co-author James T. Li, M.D., Ph.D., chair of the Division of Allergic Diseases in the Department of Internal Medicine at the Mayo Clinic, used these findings and other recent studies to shape new recommendations on safely administering this years seasonal influenza vaccine which includes protection against the 2009 H1N1 virus to egg-allergic individuals.

Drs. Greenhawt and Sanders are now leading a multi-centered study to determine the safety of this combined vaccine among patients with a history of egg anaphylaxis or a severe past allergic reaction to egg. Currently, the CDC recommends not giving the seasonal influenza vaccine to these populations. Researchers also hope to determine if the vaccine is best administered through a single dose administration instead of the graded dose method (10 percent/90 percent).

Additional U-M authors are Anna S. Chernin, MS, and Laura Howe, MD.

Reference: The safety of the H1N1 influenza A vaccine in egg allergic individuals. Annals of Allergy, Asthma & Immunology, Vol. 105, Issue 5, November, 2010.