A chance exchange of messages with a prominent GP classmate led me to understand that there may be many doctors in Singapore who are uncomfortable with providing flu shots to children with egg allergy.

The issue here is that the vast majority of influenza vaccines contain a tiny amount of ovalbumin – an egg protein – because the production of these vaccines require an egg-based manufacturing process. Candidate vaccine viruses are injected into fertilized hen’s eggs and incubated. Several days later, the virus containing fluid is harvested and the viruses are either inactivated (for inactivated influenza vaccines – IIV) with the virus antigen purified or else undergo a separate process for producing live attenuated influenza vaccines (LAIV).

Influenza vaccines are imperfect, especially with regards to their efficacy, but they are cheap relative to other vaccines and are very safe. As mentioned last year, they remain one of the most cost-effective public health strategies for preventing influenza. This is especially true in children, where a Cochrane Review updated in February 2018 estimated that vaccinating 7 children would result in avoiding one case of influenza.

The Joint Task Force on Practice Parameters in the USA (comprising 12 members of which 6 each are assigned by the American Academy of Allergy, Asthma, and Immunology (AAAAI) and the American College of Allergy, Asthma, and Immunology (ACAAI) respectively) published a practice update in 2017 with the following strong conclusion:

“There is strong evidence that egg allergic individuals can safely receive IIV (which is what is most commonly available in Singapore) or LAIV (available as nasal spray) if the latter vaccine is recommended for use once the concerns regarding efficacy have been resolved. Presence of egg allergy in an individual is not a contraindication to receive IIV or LAIV. Influenza vaccine recipients with egg allergy are at no greater risk for a systemic allergic reaction than those without egg allergy. Precautions, such as choice of a particular vaccine, special observation periods, or restriction of administration to particular medical settings, are not warranted and constitute an unnecessary barrier to immunization. Vaccine providers and screening questionnaires do not need to ask about the egg allergy status of recipients of influenza vaccine.”

This conclusion was based on additional data since 2013, comprising a total of 28 studies, 4,315 egg-allergic – including 656 with severe egg allergic – IIV recipients, where no cases of anaphylaxis had been reported. Minor reactions including hives had been reported, but the rates of these were no higher than in non-egg-allergic individuals.

Since 2016, the USA Centers for Disease Prevention and Control (CDC) and its Advisory Committee on Immunization Practices (ACIP) have recommended influenza vaccination even for those with severe egg allergies, although their recommendation is less absolute than AAAI and ACAAI’s above. The vaccine is recommended to be administered only in a setting (inpatient or outpatient) where a healthcare provider able to recognize and manage severe allergic conditions is present.

Canada’s National Advisory Committee on Immunization (NACI) had recommended that egg allergy should not be a contraindication to influenza vaccination since 2011. In a remarkably detailed report, the NACI revealed that 131 adverse events occurred in egg-allergic influenza vaccine recipients between 1997 and 2016, and both rate as well as severity of adverse events was not higher compared against non-egg-allergic vaccine recipients.

I was not able to find any national-level recommendation in Singapore, although a quick search revealed recommendations (one here in HealthHub) similar to the above – that egg allergy should no longer be considered a contraindication to influenza vaccination.

I found two further interesting review articles, although unfortunately both are behind paywalls. Here is one on egg allergy, and a second one on vaccine-associated hypersensitivity. There is an older article (2012) on egg allergy that is freely accessible here.

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About hsuliyang

I am an infectious diseases physician based in Singapore.

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Infectious diseases, Influenza, Public Health

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