Experts from the National Institute of Allergy and Infectious Diseases (NIAID) discuss how the process of preparing seasonal influenza vaccines in eggs may contribute to their limited effectiveness.
Flu vaccines are updated annually to keep up with continual changes in circulating influenza viruses. It is well-established that influenza vaccines are less effective in “mismatched” seasons when the main circulating strains change after the months-long vaccine production process has already begun. However, even in previous years when the vaccine has been well-matched to circulating influenza strains, effectiveness has been low (40 to 60 percent).
Multiple factors impact the effectiveness of influenza vaccines, such as an individual’s history of exposure to prior influenza viruses and vaccinations, age, genetics, and coexisting health problems. The authors note that manufacturing strategies may also play a significant role in reduced vaccine effectiveness. Currently, most influenza vaccines in the United States are produced using chicken eggs, while a few are made in cell culture or by using recombinant DNA technologies.