Because flu viruses mutate so fast, the only way to stop them is to destroy their ability to evolve. That's the key to creating a universal flu vaccine... and now we may have found the secret to creating one, and wiping out the flu.
There's already a bunch of potential universal vaccines for a wide variety of flu strains in development, and a few have entered clinical trials. But one class of these so-called cross-protective vaccines could prove particularly powerful in going on the offensive against the flu. According to a team of Princeton researchers, the two crucial points are making the flu less severe once you've contracted it — which would greatly cut down on the contagiousness of the virus — and more importantly, targeting the parts of the virus that are the most unchanging and least adaptable.
That may seem counter-intuitive, since the whole reason why the flu is so difficult to fight back against is its super-charged evolution. But that's the whole point — it makes no sense to go after the constantly moving target while there's something sitting right there that is nearly as important to the proper functioning of the virus.
For instance, current flu vaccines target hemagglutinin, or HA, which are proteins on the surface of the virus that attach to the host cells. At first glance, this seems like the obvious place to go to kill the virus — if it can't attach to a host, then it will quickly perish. But the problem is that these proteins are extremely adaptable, and before long the virus strain has evolved a resistance to the vaccine.
On the other hand, the new universal vaccines are designed to ignore the hemagglutinin and go after other proteins inside the virus. Because these proteins are so stable, they can't evolve under pressure in the same way that HA can, which leaves them vulnerable to much longer-lasting vaccines than the proteins on the surface. Since the hemagglutinin is still intact, the virus is still going to be able to infect people, but with its internal supply chain disrupted it can't do the same damage it would have done otherwise.
According to the researchers' models, the new universal vaccines that satisfy those two requirements — reducing the severity of flu cases and going after the least adaptable part of the virus — are set up well to reduce both the normal seasonal outbreaks and, even more excitingly, the outbreak of highly contagious new strains like the recent H1N1 pandemic. What's more, the current single-strain vaccines would still have some use, and their effectiveness would actually be strengthened by the addition of the cross-protective vaccines.
In terms of protection from pandemics, the researchers say that these vaccines should be able to work on parts of the virus that are found in pretty much all strains of flu. This means that even a completely unknown strain wouldn't be able to overcome the defenses provided by the vaccine. Indeed, if the vaccines prove particularly effective, then only about 70% of the population would need to be inoculated for a herd immunity effect to kick in, where the entire population would be effectively shielded from any new outbreak.
There's a good chance that these vaccines wouldn't be able to stop all infections, and in many cases they would simply act to reduce the severity of symptoms. But that's actually a good thing, according to lead researcher Nimalan Arinaminpathy, because this would mean that the easily controlled viral strains would be allowed to just keep doing their thing, only in a way that doesn't threaten public health. That would remove any incentive for new, more deadly strains to evolve. It's easier to control the flu than to wipe it out entirely.
"We found that by putting the brakes on flu transmission, you could also put the brakes on flu evolution. Our model illustrates how we can control the flu this way, instead of simply reacting to it every few years. You can close schools and administer our current crop of vaccines and antiviral drugs as much as you want, but never realistically enough to stop transmission over any extended period of time. With the cross-protective vaccines, we may be able to finally throw a blanket on the transmission of all flu strains over the long term in a way that can impact the virus' evolution."
Of course, nothing lasts forever, and eventually some flu strain would likely find a way to evolve around the protections afforded by these vaccines. But using a mix of universal and strain-specific vaccines over the course of several years should super-charge human immunity to these viruses, and put us in much better shape to fight off the next deadly strain. We've been playing catch-up in our evolutionary arms race with the flu for way too long - we might now have a chance to finally go on the offensive for a while.