Vaccination and egg allergy

Vaccination in individuals with egg allergy

Egg allergy is one of the most common allergies in Canada, affecting approximately 1.2% of children and 0.7% of adults.⁴ Five vaccines authorized for use in Canada are manufactured using hens’ eggs or derivatives such as chicken embryos and could theoretically contain egg protein: MMR and MMRV, influenza, Imvamune (a third-generation smallpox and mpox vaccine), yellow fever, and 1 type of rabies vaccine (RabAvert) (Table 1).^3,5,6

Measles, mumps, and rubella and MMRV vaccines. Vaccines for MMR and MMRV are grown in chick embryo fibroblast cultures; however, the vaccines themselves contain little to no egg protein.³ Multiple studies have demonstrated the safety of MMR or MMRV vaccination in individuals with egg allergy. A Canadian study conducted over an 8-year period with 500 children who had egg allergy and who were vaccinated with MMR vaccine found no cases of anaphylactic reactions.⁷ A prospective study of 54 children in the United States with confirmed egg allergy who received MMR vaccinations found no immediate or delayed adverse reactions.⁸

The authors of the prospective study also reviewed the literature and identified studies with a combined total of 1265 children with egg allergy who had received measles or MMR vaccines.⁸ Among the 1265 children who received a full standard dose of vaccine, vaccination was tolerated by 284 with egg allergy confirmed by oral challenge, by 1209 with egg allergy confirmed by positive skin testing to egg, and by 1225 with a history of egg allergy. The authors concluded that more than 99% of children with egg allergy can safely receive MMR vaccines (95% CI 99.41 to 99.98).⁸ The Canadian Immunization Guide (CIG), which was developed based on NACI recommendations, advises that MMR or MMRV vaccines can be administered in a routine manner in individuals with egg allergies without allergy consultation, skin testing, or prolonged observation.^6,9 The JTFPP similarly supports the safety of MMR or MMRV vaccination in individuals allergic to eggs without any special precautions or testing.³ For these individuals, referral to an allergist prior to vaccination is not necessary.

Influenza vaccines. As with MMR and MMRV vaccines, most influenza vaccines are grown in chick embryo fibroblast cultures and may contain residual egg protein.⁶ However, studies have consistently demonstrated the safety of influenza vaccination in individuals with egg allergy. A JTFPP review of 28 studies (with a total of 4315 individuals with egg allergy, including 656 with a history of anaphylaxis) found no cases of anaphylaxis following influenza vaccination.¹⁰ The JTFPP review included 3 prospective studies from Canada.^11-13 Both the CIG and the JTFPP advise that influenza vaccine can be administered in a routine manner in individuals with egg allergies without any special precautions or testing and irrespective of the severity of a patient’s previous allergic reaction to egg.^6,10

Smallpox and mpox vaccine. Imvamune vaccine (a third-generation smallpox vaccine and the only vaccine in Canada approved for mpox protection or post-exposure prophylaxis) is grown in chicken embryo fibroblast cells and contains potential trace amounts of egg.¹⁴ However, the theoretical risk associated with this trace amount of egg is thought to be low. Both the Canadian Society of Allergy and Clinical Immunology and the CIG recommend that Imvamune can be used in individuals with egg allergy in any setting where vaccines are routinely administered, although prolonged observation (30 minutes) may be considered owing to lack of data.^6,15

Rabies vaccines. There are 2 approved rabies vaccines in Canada—Imovax (inactivated human diploid cell vaccine) and RabAvert (inactivated purified chick embryo cell culture vaccine).¹⁶ As RabAvert, but not Imovax, is grown in chick embryos, the CIG recommends Imovax for use in individuals with egg allergy for both preexposure and post-exposure prophylaxis, on the basis of a theoretical increased risk of anaphylaxis.⁶ For post-exposure prophylaxis, if Imovax is not available RabAvert can be considered in individuals with egg allergy and followed with medical monitoring.⁶

Yellow fever vaccine. Anaphylaxis following yellow fever vaccination in individuals with egg allergy has been reported (although these incidents are rare).¹⁷ Accordingly, the CIG recommends that all individuals with egg allergy be referred to an allergist for evaluation prior to vaccine administration.¹⁸ Should an individual with egg allergy require yellow fever vaccination, desensitization protocols exist,³ and recent evidence supports the safety of such desensitization protocols in individuals with egg allergy.¹⁹

How to manage acute allergic reactions

While local and mild reactions following vaccination are common, anaphylaxis is very rare and is estimated to occur at a rate of 1 to 1.3 episodes per million doses of vaccine administered.^3,5 As anaphylaxis is rapid in onset (often within minutes of vaccination),²⁰ any vaccine recipient should be observed for at least 15 minutes following vaccination.⁵ Anaphylaxis management kits should be available at all vaccine administration sites, and all vaccine providers should be educated in the recognition and management of anaphylaxis. Signs and symptoms of anaphylaxis include cutaneous (urticaria, angioedema), respiratory (cough, wheeze, dyspnea), gastrointestinal (vomiting, diarrhea), and central nervous system (irritability, sense of impending doom) manifestations.^5,21 Should a systemic allergic reaction occur following vaccination, initial management steps include activating emergency medical services, placing the individual on their back, and administering an intramuscular injection of epinephrine (0.01 mg/kg body weight of a 1:1000 [1 mg/mL] solution) in the mid-anterolateral thigh.⁵ The CIG provides further information for health care providers about management of anaphylaxis.⁵

All individuals with allergic reactions following vaccination should be referred to an allergist or other qualified health care provider for further evaluation. In addition, all individuals with egg allergy should be referred to an allergist for management of the allergy. Finally, anaphylaxis has many mimics, including immunization stress–related response, which should be considered whenever an immediate reaction occurs after vaccination.²²