The traditional method for developing a vaccine uses substrates isolated from chicken eggs or mammalian cells. This method has several drawbacks that could pose many problems. The first major issue is the time taken to develop a vaccine using this method, which could be longer than six months. The nature of the disease agent can present significant challenges to cell- and egg-based production depending on the species and strain of the agent. Moreover, there is a concern that people with allergies to eggs may also react negatively to an egg-based vaccine. Using modern plasmid DNA-based vaccines to combat infectious diseases is an alternative to traditional egg-based and mammalian-based vaccines. This article compares these two methods of developing and producing vaccines.
Another concern regarding the production of vaccines in chicken eggs is that production capacity is limited to the number and availability of specific pathogen-free fertilized eggs and the finite capacity of current manufacturing facilities. For example, with the influenza vaccine, one egg is required for each dose of vaccine. Therefore, for a million doses, a million chicken eggs must be processed. This method is not ideal for rapid large-scale production scale-up requirements. The specific strain and species of the disease also can present challenges to the actual production of the vaccine in embryonated eggs. Certain virus strains may not replicate productively in an embryonic avian host, which can then require additional process optimization and production time. For example, the H5N1 strain of the avian influenza is generally deadly to chicken embryos and therefore, an alternative method must be employed for the production of the vaccine.6 In addition, even for avian flu strains that could be produced in chicken embryos, in the event of a pandemic, the availability of eggs would be severely impacted. Another disadvantage of producing vaccines in eggs is that people with allergies to eggs may react negatively to egg-based vaccines.