WASHINGTON – The good news is that flu season has finally peaked.
Outpatient visits for influenza-like illness dropped from 6.4 percent of all recorded visits to 5 percent during the eighth week of the year, according to the latest data from the federal Centers for Disease Control and Prevention. That said, the agency’s report notes that the flu is still widespread in 45 states, with 114 pediatric deaths reported so far this season.
As of now, this year’s seasonal flu vaccine seems to be about 36 percent effective. In a previous article, we highlighted the challenges researchers face trying to boost that effectiveness, part of the hunt for a so-called “universal” flu vaccine.
To recap: It’s going to be quite difficult to make a universal vaccine, particularly because “universal” means more than one thing.
There’s universal in the sense that the vaccine targets the flu’s many different strains, and there’s universal in the sense that it lasts for more than one flu season – preferably for life.
But scientists have some strategic tools in their arsenal. Here’s a look at two universal vaccine candidates in clinical trials right now, and how they work with our immune system in its ongoing fight against the flu.
The American front: boosting B cells
Our bodies mount a multi-tiered response when confronted with viruses like influenza. One of the primary players in that response is the B cells, which produce antibodies that target the flu’s front ranks, particularly a protein called hemagglutinin found on the surface of the flu.
Imagine hemagglutinin like a mushroom: a head and a stalk. The head is the outermost part of the protein. Our bodies naturally target it, and thus so do our typical seasonal flu vaccines. But it’s always changing, meaning that each time we encounter the flu, we encounter a slightly different strain of the flu. This makes it very difficult for scientists to develop a vaccine to thwart it in any given season, let alone more than one season.
The hemagglutinin stalk, on the other hand, stays consistent among strains, but it’s harder for our B cells to target. “So how do you convince the immune system to make an antibody response against the stalk?” says Florian Krammer, a researcher at the New York-based Icahn School of Medicine at Mount Sinai. The team he’s working with may have figured out one way.
Their vaccine is a multi-dose “prime-boost” vaccine, similar to the measles-mumps-rubella and tetanus vaccines. The two doses – prime and boost – prime the body to recognize the virus and boost its response to the virus so that it lasts for many years.
In the case of this vaccine, each dose, prime and boost, contains the same hemagglutinin stalk spliced with a different hemagglutinin head. Through this same-stalk/different-head strategy, the person’s body theoretically learns to recognize and target the virus by the stalk, which is conserved among flu strains, rather than just the ever-changing head. So if the vaccine works, it could target the many strains of flu for many years.
The Mount Sinai group’s vaccine has been tested successfully in animals, and now it’s in its first human safety trials through a partnership with several nonprofits and industry partners.
The British front: maximizing T cells
Across the pond, researchers at Vaccitech, a University of Oxford-affiliated vaccine development company, have a different strategy to target the flu. This one makes use of our body’s T cell response.
The T cells’ job is to find the cells in our body that have already been invaded by the flu, and to destroy those cells so they don’t replicate and spread the virus.
Vaccitech’s vaccine boosts the numbers of the body’s T cells that remember the flu’s innermost proteins. Those proteins are deeper than the surface hemagglutinin that the Mount Sinai team is targeting. But, just like the hemagglutinin stalks, the inner proteins are the same among flu strains. So theoretically, Vaccitech’s vaccine could protect against all of the flu’s primary circulating strains.
On top of that, T cells help stop transmission of the virus between people, says Sarah Gilbert, a Vaccitech co-founder and one of the team’s lead researchers. Boosting people’s T cell responses, then, could help protect not just individuals, but whole populations.
Vaccitech’s vaccine is in Phase II trials in the U.K., which means it’s been proved safe and now will hopefully be proved effective. Its target demographic is the 65-and-over population, which Gilbert notes “bears the brunt” of influenza illness and often isn’t helped by seasonal vaccines. “So we hope to really make a difference for this age group,” she says.
We wait. (And get the seasonal flu vaccine while we do so.)
Vaccine development requires quite a bit of financial and human resources, Krammer notes. The two vaccines highlighted here are only in early trial stages, and still have to be proved effective in humans. So it will be years before they could become everyday realities.
To be sure, we’re much further along now than we were a decade ago. Technological advances in the last 10 to 15 years have provided researchers with the basic knowledge about influenza immunology they need to begin developing universal vaccines, says Krammer.
But developing those vaccines is a herculean task. “You need endurance to do it,” Krammer says, “because it takes a very long time.”