Influenza — which people commonly refer to as “the flu” — is one of the most widespread illnesses worldwide.
Two virus strains — influenza virus strain A and strain B — are responsible for the flu. This disease has led to between 9.3 million and 49 million estimated cases of illness each year since 2010 in the United States alone, according to the Centers for Disease Control and Prevention (CDC).
As there are different viral strains, and each strain has many different subtypes, doctors must administer the correct vaccine each time. They need to use one that targets the specific strains and subtypes that are circulating in the population for this preventive approach to be successful.
So far, there has been no “universal vaccine” that can target all influenza viruses effectively. But are researchers getting closer to developing one?
Source: Scientists may be getting closer to creating a universal flu vaccine : Medical News Today