Paul A. Offit, MD

Posted: 09/08/2011

Hi. My name is Paul Offit and I'm speaking to you from the Vaccine Education Center at the Children's Hospital of Philadelphia. Today I thought we would talk about some recent developments regarding the influenza vaccine.

The original injectable influenza vaccine was developed by Thomas Francis at the University of Michigan in the mid-1940s. He made that vaccine by taking influenza virus, injecting it into embryonated hen's eggs, and letting the virus grow in the chorioallantoic cells that surrounded the yolk sac. He would then harvest the egg, purify the virus, and kill the virus with formaldehyde. But because the vaccine was made in eggs, a certain amount of contaminating egg protein, specifically, ovalbumin was always still present.

When Mossad made the live attenuated influenza vaccine, also at the University of Michigan, he also cultivated the virus in egg, so the live attenuated vaccine is, to some extent, contaminated with egg proteins such as ovalbumin as well.

What do we do, then, about children and adults who are severely allergic to egg proteins? Until very recently, the influenza vaccine has been contraindicated for those allergic children and adults [except for those with egg allergy who were at risk for severe complications of influenza]. However, during the last 15 years, we have gotten much better at protein purification, protein chemistry, and being able to purify the inactivated virus or the live attenuated virus away from ovalbumin. Thus, there is much, much less ovalbumin in current vaccines. We are beginning to see a change in that safety issue so that now, children who have egg allergies, even severe egg allergies, can get the vaccine. [The Advisory Committee on Immunization Practices] does recommend that, as a precaution for those who have more severe allergic manifestations like hives (or worse), those children should be given the vaccine in the presence of an allergist or someone who knows what to do should there be an anaphylactic reaction.^[1] I think ultimately we will reach a time when egg allergy is not a contraindication to that vaccine.

This is reminiscent of what happened with the measles and mumps vaccines, which were grown not in eggs but in chick embryo fibroblast cells. There also were some contaminating egg proteins, although logarithmically less than were contained in the flu vaccine. But Hugh Sampson and others have shown that even people with severe egg allergies who get the measles or mumps vaccine do not have a problem. I think that is where we are heading with the influenza vaccine.

At the end of June, the Advisory Committee on Immunization Practices^[1] stated that the influenza vaccine is not contraindicated for any children with egg allergy, not just those who are at risk for severe complications of influenza. Ultimately, I believe we will give the influenza vaccine much as we give the measles vaccine to children who are egg allergic now. Thank you for your attention.

1. Prevention and Control of Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2011. MMWR Morbid Mortal Wkly Rep. [Early release: August 18, 2011.] Available at: https://www.cdc.gov/mmwr/preview/mmwrhtml/mm60e0818a1.htm?s_cid=mm60e0818a1_w Accessed August 22, 2011.

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