Myth Busters: Egg-Based Vaccine Production

Despite continual advances in the technology, misconceptions remain about the validity and effectiveness of egg-based vaccine production

By Ken Christiansen, president of RAME-HART

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Vaccines serve as a critical line of defense in disease prevention and control. As global communities interact more, there is a pronounced importance on rapidly delivering greater quantities of vaccine that reach more people as quickly as possible.

Health organizations are increasingly concerned about the potential of an influenza virus pandemic amidst a growing global population. This fear has been exacerbated by the 2009 H1N1 (swine flu) epidemic and more recently, the H7N9 (avian flu) outbreak in China¹. The latter is a stark example of how this threat affects livestock and humans alike. Developers of both human and veterinary vaccines must address this challenge and deliver superior protection in shorter periods of time.

As new technologies are explored, health organizations stress the severity of an impending influenza epidemic. In 2005, the United Nations System Coordinator for Avian and Human Influenza outlined a global initiative designed to prevent the potentially devastating impact of an influenza virus, which could cause anywhere from five to 150 million deaths². Alternatives such as cell-culture-based growth systems, recombinant protein expression systems and DNA-based vaccines face several limitations (e.g., tumorigenicity risks, ongoing clinical development, simply being cost-prohibitive) that would currently not make them viable options in the event of a pandemic³.  

Chicken-egg-based influenza vaccines, in contrast, remain the most effective manufacturing method available. As a part of its H7N9 preparedness strategy, the CDC is currently distributing viral samples grown in eggs to develop a vaccine. The H7N9 avian flu virus samples have been replicating well in eggs according to CDC reports4. The process is highly regulated, stable and predictable. Nonetheless, despite continual advances in the technology, misconceptions remain about the validity and effectiveness of egg-based vaccine production. In the following article, we discuss and evaluate the ‘myths’ around this proven vaccine development process.

Myth #1: “Egg-based Influenza Vaccine Production is Slow and Outdated”
Egg-based vaccine production is on occasion characterized as outdated and old-fashioned. Originally developed in the 1950s, the technology has been used to produce seasonal influenza vaccines for more than 30 years. While long-standing, the process has evolved to address various challenges, including yield, automation, capacity, quality assurance and production speed. Improvements to egg supply variability have also been made, minimizing and often eliminating the periods of time that eggs were previously unavailable5 for use. 

One area where this mistaken perception arises is in the face of pandemic preparedness. Inadequate vaccine supply is an industry-wide challenge but egg-based production comes under duress from the belief that livestock management is an erratic, un-evolved process. Vaccine manufacturer Sanofi Pasteur, however, recently developed new technologies to improve egg supply and increase availability in advance of vaccine production dates.  With the advent of restructured flock management, embryonated eggs, previously unavailable for certain periods of time, can now support vaccine production year round4. 

Newer manufacturing methods such as cell-based production are predicated on improving areas like speed-to-market, risk of contamination and vaccine potency. But cell-based vaccines undergo many of the same critical processes as the egg-based method such as vaccine isolation, extraction and purification. Furthermore, in cell-based technologies, the use of animal cells in media is disadvantageous because of concerns over bio-burden potential and batch variability – two factors which compromise viral yield.  Another shared concern is strain variability. Because of the influenza virus’ propensity to change composition, trivalent vaccines that consist of different influenza strains must be formulated annually. While cell-based production is designed for faster response, it is still subject to the physical constraints of strain availability4. 

As a pioneer of inoculating and harvesting machines, RAME-HART has continuously developed advancements in egg-based vaccine production technologies. Thirty years ago, egg-based production was completely manual and very labor intensive. However, over time, RAME-HART has automated multiple steps in the manufacturing process including harvesting and inoculation, reducing the frequency of human error, bio-burden and the risk of contamination. Egg-based influenza vaccine production has gone from a manual operation to an almost completely automated process where eggs are loaded, inspected, inoculated, de-capped, harvested and unloaded without virtually any human interference. 

Advances to the egg-based process like recombinant vector technologies are being explored to develop faster response times to an impending influenza pandemic. This method manipulates an adenovirus capable of infecting embryonated eggs to produce recombinant proteins. These egg recombinant technologies are designed to increase harvesting yields, reduce the cost of production and abridge the time of full-scale influenza vaccine production from 28 weeks (the standard timetable) to 20 weeks6. 

Overall, egg-based flu vaccine manufacturing has continually evolved, stabilizing egg supply variability, increasing vaccine yield, reducing human error, minimizing the incidence of bio-burden and raising production capacity.

Myth #2: “Egg-based Influenza Vaccine Manufacturing is a Messy, Error-filled Manual Process”
As we have already seen, egg-based vaccine production has evolved beyond a completely manual process. Increased automation and advances in technology have now cut down on limitations caused by human involvement – physical manipulation, potential of increased bio-burden, damage to the egg supply and subjective evaluation of egg suitability. Nonetheless, egg-based production is often characterized as a primitive process marked by broken egg shells and spilled yolk.

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