As an RNA virus, influenza is highly variable. Even subtypes, the virus’s genetic code continues to mutate, leading to dramatic changes between quarters and quarters, known to scientists as “antigen drift.” Because of the dramatic changes, the vaccine for the last flu season could not be used for the next flu season.
To combat antigen drift, scientists constantly adjusted the vaccine and designed to respond to the influenza virus encapsulation protein known as hemagglutinin, targeting the protein’s head. But the head has a variable tendency, and its stem is less prone to mutation. Therefore, the flu vaccine for the stem of blood cells can be effective against all subtypes of the virus and still work under antigen drift.
The vaccine is also universal. A candidate generic vaccine developed by NIAID is in the first phase of clinical trials, with results to be announced earlier this year.