In the wake of the COVID-19 pandemic, a series of vaccines emerged with what seemed to the general public like lightning speed. In truth, those developments were made possible by the decades of research that came before, which focused on the development of a universal influenza vaccine.

 We refer to the disease caused by all strains of influenza with the same colloquial moniker—“the flu”—but there are in fact four different types of influenza viruses (A, B, C, and D). These types are then divided into many subtypes based on the two proteins that cover the surface of the virus (hemagglutinin and neuraminidase, which is where flu viruses get their infamous “H” and “N” labels). Vaccines can target certain subtypes, or groups of subtypes of flu viruses, but protecting against all strains of influenza with a single vaccine is a medical breakthrough that is yet to be achieved.

 Flu viruses, like all viruses, are subject to both “antigenic drift” and “antigenic shift,” two modes by which flu viruses mutate, and consequently, seasonally evade the body’s immune system (the more substantial “antigenic shift” occurs only in type A viruses, which is why these are the viruses known to cause pandemics). These constant mutations make the cultivation of a universal vaccine incredibly challenging, but scientists have had several breakthroughs that might be pointing them in the direction of a solution.
 
While vaccines have historically targeted the head of hemagglutinin proteins, developing vaccines are triggering antibodies that bind to the stalk or the neck of the protein—a section of the protein subject to much less variation. Nanoparticle flu vaccines are also being studied as a possible key to unlocking the next generation of vaccines and making viral protection broader than it’s ever been before. For a deeper dive into this groundbreaking nanoparticle technology, click here.