Flu Vaccine Effectiveness: Alternatives to Chicken Egg Production

For decades, the influenza vaccine has been produced using chicken eggs, a method established since the 1940s. While this traditional technology has proven effective, it has limitations, particularly in adapting to the rapidly changing flu virus.

Dr. Lynora Saxinger, an infectious diseases specialist at the University of Alberta, highlighted that flu viruses can adapt to grow better in avian cells, potentially reducing vaccine effectiveness against human strains.

According to the World Health Organization, vaccine strain decisions are made biannually, requiring six months for production, which hampers timely responses to circulating flu variants. This year, the New England Journal of Medicine published a Phase 3 clinical trial led by Pfizer that tested an mRNA flu vaccine against the traditional egg-based vaccine.

The study, involving over eighteen thousand adults in the U.S., South Africa, and the Philippines during the 2022-23 flu season, found the mRNA vaccine to be thirty-four percent more effective. Dr. Matthew Miller, director of the Degroote Institute for Infectious Disease Research at McMaster University, emphasized the significance of this finding as a proof-of-concept for future mRNA vaccine development.

However, mild to moderate side effects, such as fever and chills, were reported more frequently among recipients of the mRNA vaccine. Angela Rasmussen, a principal research scientist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan, noted the importance of addressing public concerns regarding mRNA technology amidst ongoing disinformation.

Traditional egg-based vaccines involve growing the virus in eggs and inactivating it chemically, while cell-based vaccines, which can be produced more quickly, use dog kidney cells instead. Dr. Barry Pakes of the University of Toronto pointed out that while more efficient, cell-based vaccines are significantly more expensive.

Another innovative approach includes recombinant vaccines, where a part of the virus is produced in insect cells. Dr. Miller also mentioned ongoing research into inhalable vaccines that aim for stronger, longer-lasting protection against both seasonal and pandemic influenza.

Despite these advancements, experts predict that egg-based vaccines will continue to dominate the Canadian flu vaccine supply for the foreseeable future, as they have historically provided effective prevention against severe illness.