Avian influenza and egg-derived vaccines: Should we be concerned?

Author(s):  Dr Sherilyn Houle

Highly pathogenic avian influenza A H5N1 [HPAI-A(H5N1)] has affected 108 countries across 5 continents as of December 2024, including 500 bird species and 70 mammalian species.¹ While the risk to humans is currently low and cases in humans have been largely among dairy and poultry workers,² concerns about its impact on egg supply and prices exist due to the need to cull infected flocks to reduce its spread.³

A number of vaccines used to protect travellers are manufactured using eggs, including some vaccines against influenza, measles/mumps/rubella, and rabies, and the yellow fever vaccine.⁴ Health professionals and patients may have questions about what, if any, impact HPAI-A(H5N1) may have on the availability of these vaccines.

The short answer is that any impact is expected to be relatively small. A survey of influenza vaccine manufacturers in 2023 identified that while access to egg supply in the event of a pandemic or high off-season demand can affect production capacity, 70.7% of manufacturers producing egg-based vaccines expect to have adequate access to eggs and ancillary supplies to achieve maximum vaccine production and 58.7% have standard operating procedures in place to source eggs or ancillary supplies in an off-season in the event of a pandemic. Some have also indicated the ability to switch to cell-based manufacturing if required.⁵ However, local production and access varies worldwide, with influenza vaccine manufacturing capacity noted across all World Health Organization regions at that time except for the African Region, with an over-representation of manufacturing capacity in high and upper-middle income countries.⁵

Health professionals and patients should also be aware that pharmaceutical-grade eggs used for vaccine production are not sourced from the food supply; rather, these flocks are highly regulated and insulated to reduce the risk of the introduction or spread of infectious diseases. Regulations include strict cleaning, decontamination, and transport standards, the use of personal protective equipment by workers, and air flow and HEPA filtration measures.⁶

As we learned from COVID-19, it is difficult to fully predict the impact of a pandemic on various supply chains; however, there does not currently appear to be a cause for concern when it comes to egg-based vaccine production.

References

[1].  Avian flu reported in 108 countries across five continents, says UN health agency (17 December 2024).  United Nations [Link]
[2].  H5 bird flu: current situation (21 March 2025).  Centers for Disease Control and Prevention [Link]
[3].  Explainer: How bird flu has sent US eggs prices skyrocketing (21 February 2025).  Reuters. Polansek T, Douglas L [Link]
[4].  Contents of immunizing agents authorized for use in Canada (6 February 2025).  Public Health Agency of Canada [Link]
[5].  Global production capacity of seasonal and pandemic influenza vaccines in 2023.  Taaffe J, Goldin S, Lambach P, Sparrow E ‐ Vaccine 2025;51:126839 [Link]
[6].  WHO biosafety risk assessment and guidelines for the production and quality control of human influenza pandemic vaccines.  World Health Organization [Link]