Long-lasting flu vaccine could replace yearly shots

November marked the start of flu season in the Northern Hemisphere. So if you haven’t gotten your flu shot yet, now’s the time. Unlike other vaccines that people may only need once in their lives, flu shots must be given yearly (to account for the ever-morphing virus it targets). But that soon may change. Researchers have just developed a vaccine that protects against many more types, or strains, of the flu virus. Its benefit? These shots might be able to confer lifelong protection from flu.

A flu shot can help you avoid fever, aches and fatigue that are no fun. But influenza poses far bigger risks for people who are very young or very old, or who have a weak immune system. For them this viral infection can be deadly.

U.S. statistics show how variable the risk of flu mortality can be from year to year. In some flu seasons, as few as 3,000 flu victims may die. Other years are far worse. Roughly 56,000 U.S. residents died from flu during the winter of 2012 to 2013.

Flu shots are the best defense against these infections. These vaccines teach the immune system how to identify a flu virus. That lets the body respond quickly to quash an infection before it can take hold.

But the flu virus evolves rapidly. The strains most likely to infect people this year will be different from last year’s major strains. If your immune system doesn’t recognize the latest version, you could get sick.

So scientists create new vaccines each year to target the latest variants. That’s why people need a new shot each year. But researchers at the University of Nebraska–Lincoln have developed a new vaccine that could last longer. To create it, they probed the genes of flu viruses and then “rewound” their evolutionary clock.

Hunting viral ancestors

Eric Weaver led the team. As a virologist, he studies viruses and how they affect the body. His group started by figuring out what the ancestral flu virus might have looked like. From what they learned, these researchers hoped to partially recreate some shared ancestor of today’s flu strains.

If two people trace their family trees back far enough, they will find a shared ancestor. That’s what Weaver and his team did with genes in the flu viruses. They traced them back to find genes from an ancestor that modern flu strains share in common.

There are 18 subtypes of flu, Weaver notes. The researchers worked with just four. These are the strains most likely to cause disease outbreaks in people. The scientists analyzed the viruses’ genes. From these, they created an average set of flu genes and put them into an artificial virus. This new virus might resemble the ancestor to the four modern strains.

Next, they created a vaccine to their artificial virus. To do this, they altered the genes so that they couldn’t cause illness. Then they inserted these into yet another virus. That recipient virus is called a vector. It can insert genes into cells. For their vector, the scientists chose a virus that causes the common cold.

That vector had been changed so it couldn’t make people or animals sick. Yet it could still insert its DNA into a host’s cells. That trait was important. (Viruses can’t reproduce on their own. Instead, they inject their genes into a host animal’s cells, which forces those cells to copy the virus.)

The researchers used their vector to deliver their new vaccine into cells. That triggered an immune response to the ancestral virus.

Powerful protection

The team then tested its vaccine in mice. Some mice got a low dose of the vaccine (similar to what people might receive). Others got a high dose of it. A third group got a high dose of FluMist. This is a standard flu vaccine that’s not delivered as a shot. (It’s instead spritzed up the nose.) A final group of mice got a high dose of FluZone, the annual flu shot.

Four weeks later, scientists exposed the mice to one of nine different flu strains. Each mouse received enough virus to kill five to 50 mice, Weaver says.

Mice vaccinated with FluMist or FluZone died. These vaccines could not protect them from those heavy doses of virus. But mice that got the new vaccine were protected. Those getting a low dose of vaccine survived seven of the nine viruses.

“Mice are extremely well protected by this vaccine,” Weaver concludes.

Many studies have focused on how well just one part of the immune system responds to a flu vaccine, notes Matthew Miller. He was not involved with the new research, but he’s familiar with such studies. Miller’s own work at McMaster University in Ontario, Canada, focuses on immunity to viruses. Most studies in this field look at how well the body makes antibodies — a class of proteins — in response to the vaccine, he says. Those immune proteins help tag infected cells, he explains. But the ancestral-flu treatment stimulated other parts of the immune system, too. He suspects that difference “is really critical to having a vaccine that works well.”

When might the new vaccine be ready to give to people? It could be a while, Weaver thinks. One potential hurdle is those cold viruses commonly used as vectors. By the time people reach age 18, anywhere from one-fifth to half of them will already have been exposed to those viruses, Weaver says. So their immune systems may attack those vectors before they can help them the body build up a defense against influenza.

If scientists can overcome that challenge, however, a treatment like this one might one day replace yearly flu shots. “If we can use it as a childhood vaccine,” Weaver says, “we may be able to set up potentially life-long immunity.”