Mutation lowers potency of flu vaccine
January 18, 2018 -- Genetic changes during vaccine production in chicken eggs resulted in flu shots that failed to protect against the H3N2 virus strain.
Influenza viruses are continually changing. One way they mutate is by “antigenic drift” -- small changes to the genes that happen as a virus replicates.
Innoculations of flu vaccines, containing inactivated viruses, alert the human immune system to produce antibodies to fight the real thing.
In the case of this year’s flu epidemic, the vaccine included an influenza A strain, H3N2. Researchers found that antigenic drift had mutated one of its surface proteins by attaching it to a sugar molecule. The sugar made it difficult for antibodies to bind to the protein and helped the virus avoid destruction.
For decades, most flu vaccine strains have been grown in fertilised chicken eggs which stimulate excellent yield. But it is known that viruses can adopt genetic changes that help them replicate in eggs.
The sugar molecule restricted the virus’s ability to grow in an egg environment, so the virus mutated again to dump the sugar molecule. This egg-induced mutation decreased the ability of antibodies to attach to and destroy the flu virus.