As the weather gets colder and the days get shorter, many people will be going to their clinic or pharmacy to receive their seasonal flu shot. While the flu shot is a once-a-year concern for most, the effort to create a more effective influenza vaccine has long been a concern for researchers and health professionals.
In recent years, the effectiveness of the flu vaccine has declined and some have linked this decline to egg-based creation of flu vaccines. A group of scientists working at The Scripps Research Institute (TSRI) now believe they have uncovered the reason for this.
According to a paper published last week in PLOS Pathogens, when flu vaccine is created using the traditional method of injecting influenza into chicken eggs to replicate and later be purified, the virus tends to favor mutations that are ideal for the egg environment.
The influenza subtype examined in the study is H3N2, known to mutate when grown in chicken eggs. The researchers used X-ray crystallography to show that a key protein receptor of H3N2 tends to mutate to better attach to chicken cells when grown in an egg.
This mutation, called L194P on the virus's hemagglutinin glycoprotein (HA), lowers the ability of the vaccine to trigger an effective immune response when administered to humans. The authors caution that this mutation should be monitored in creating new flu vaccine and that alternative methods for flu vaccine creation should be explored to avoid such mutations.
Image: The L194P egg-adaptive mutation dramatically increases the motility of the major epitope on the hemagglutinin of influenza H3 viruses. Red: high motility; white: medium motility; blue: low motility. Image courtesy of the Wilson Lab.