Why a Universal Flu Vaccine Eludes Us—For Now

Virologists have long sought a simple and effective vaccine for influenza. A quick glance at thee stats reveals why: Every year, the virus sickens up to 10% of the global population and kills up to 500,000 people. Now, scientists have an idea why one form of universal flu vaccine has eluded them, but others are still speeding toward trials.

In a study of 21 people’s immune responses to influenza, immunologists discovered that while our immune system can easily identify the part of the virus that’s easily changed from year to year, it all but ignores the bits that are conserved. Because of that, our immune system’s B cells are duped time and again into thinking the virus is entirely new—and cranking out new antibodies in response—even when only minor mutations have occurred.

young-boy-flu-mask
A young boy wears a mask for protection during the 2009 influenza pandemic.

Here’s Beth Mole, writing for Ars Technica:

Those virus-finding antibodies generally identify the flu by recognizing their hemagglutinin (HA), a sort of lollypop-shaped protein that allows the virus to latch onto and invade certain human cells. The outside of each virus is coated with copies of HA, with their simple stalks jutting from the viral surface and a sticky head reaching out for cells.

Most antibodies go after the easy-to-grab HA head. But the head mutates frequently, allowing it to escape antibody detection. The stalk, on the other hand, is a little harder for antibodies to get to—as the antibodies have to push past a canopy of HA-heads—but the stalk doesn’t change much from virus to virus.

Our antibodies excel at binding to the HA heads, but don’t fare nearly as well in binding to the stalks. As a result, the immune system preferentially produces head-seeking antibodies. It’s a tendency that also seems to increase with exposure to more strains of the flu.

“Even if you had an effective stalk-based vaccine, there are very few memory B cells that could be recalled to have an effective stem-based approach,” Ted Ross, professor of infectious disease at the University of Georgia, told NOVA Next. “The issue is you’re going to have to figure out a way generate and recall the very small pool of these B-cell memories that are there because the head is so dominant.”

Fortunately, the stalk-based approach isn’t the only way to a universal flu vaccine. For example, earlier this year, Jeffrey Taubenberger, a virologist at the National Institute of Allergies and Infectious Disease, published a paper where he successfully vaccinated mice with a sort of cocktail loaded with HA heads from a number of different strains of the virus. Protection was as high as 94%.

While Taubenberger’s study just looked at mice, scientists are making progress on a universal flu vaccine for humans. “There will be lots of universal flu vaccine stories coming out in 2016,” Ross said. “They’re now beginning to move towards the clinic.”