Trying for a Flu Twofer

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One reason COVID-19, or the coronavirus, has alarmed so many people is that it is a novel virus. That is, it is new to scientists.

Influenza viruses are hard to figure out anyway. They are quick-change artists. They constantly mutate, and those frequent changes make it difficult for our bodies to recognize them and fend them off.
That’s why a new flu vaccine is needed every year.

The outside of influenza A viruses are studded with two proteins called hemagglutinin and neuraminidase. There are many versions of these proteins. The combinations of each “H” and “N” give flu its name, like with the common H3N2 and H1N1 viruses that are part of every year’s flu vaccine.
Hemagglutinin helps the virus attach to cells in the nose, throat, or lungs. This is the key to getting infected. But if the immune system recognizes a particular hemagglutinin, from either an earlier infection or vaccination, it will produce flu-fighting antibodies to block the virus from latching on.
As influenza virus spreads, it gradually undergoes subtle genetic mutations (or changes). Eventually, with enough changes, defenses the body has built up in the past can no longer recognize the new strain. That’s called antigenic drift, and it’s why the flu vaccine gets an annual update.

But every so often influenza undergoes a sudden, major genetic change, resulting in a flu strain so different that most people have little or no immunity. That happened during the 1918 Spanish influenza pandemic.

A pandemic is a disease that has spread to many parts of the world. Pandemics can happen if, for example, a virus carried by a bird or a pig mixes and swaps genetic material with a typically human strain, infecting people with a novel virus. That’s called an antigenic shift. Sometimes, an animal strain jumps directly into a human.

Global health experts select the recipe for each year’s flu vaccine based on predictions of which strains are most likely to be spreading the following winter. And they hope the flue doesn’t “drift” enough that season to spoil the match. Seasonal flu vaccines won’t protect people in a pandemic like the present coronavirus.

Scientists are working to create a universal vaccine. Such a shot would protect against both seasonal flu variations and upstart viruses like COVID-19.

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