It can be said that the most important public health achievement of the past century has been vaccines. There can be no way to overemphasize the importance vaccines have had in preventing child mortality, improving quality of life, and lengthening life span. Diseases that killed millions are now a distant memory: smallpox has been completed eradicated and polio is close on its way. And now we even have vaccines that help prevent cancer!

So what does the future hold for vaccines? Would you believe us if we said that one day, the flu, HIV, and even Alzheimer’s could be prevented by just a stick of the needle?

In order to understand why some vaccines work and others don’t, we have to take a look at how vaccines function with the immune system.

A basic vaccine contains some form of the virus, whether paralyzed or dead. Once injected, the vaccine spurns the immune system to react and produce antibodies, just as it would for a real infection. The immune system has a strong memory, so it remembers any antibody it has already identified to be effective. The next time it encounters that virus, it can ramp up the antibody production in hours and prevent illness.

However, some viruses—such as HIV, the rhinovirus (which causes colds), and influenza—cannot be vaccinated against yet. The viruses evolve so quickly and mutates into so many strains in the population that the antibodies made against them do not work for a second infection.

But new discoveries and techniques may just make these vaccines possible in the near future.

For instance, take the flu. While we have a vaccine currently, it needs to be produced each year using predictions of how the virus will transform. Researchers take the best several predictions and make a cocktail vaccine. But it still doesn’t cover all the possible strains so hundreds fall sick every year. But scientists have recently determined that the reason your body can’t fight off a broad range of flu viruses has to do with pre-existing immunities to other flu strains. Once they altered the vaccine to adjust for this, they found positive results in animals that were already immune to a flu virus. Human trials are already being planned and underway.

Another group of scientists is taking a different, more conventional approach. By identifying the part of the virus that doesn’t change during reproduction and evolution, they can focus the immune system and help it target a wide range of flu viruses. This one-time vaccine would be particularly helpful in getting a large portion of the population vaccinated and would be much safer for people with weaker immune systems, such as the children and elderly.

This approach has also been tried in the past with HIV. A highly promising trial in monkey from last year used a vaccine that relied on a part of HIV that rarely changes as the virus reproduces. The trial also gave strong evidence that the immune system uses two distinct mechanisms, killing the virus and preventing the virus from replicating. A brand-new technique was patented just two months ago that targets replication.

But it’s not just killer viruses that can be prevented by vaccines. Scientists are also on the verge of developing a vaccine for preventing Alzheimer’s. In a study published just days ago, researchers describe how a new Alzheimer’s treatment could both prevent people from developing the disease and keep the illness from getting worse in people who already have it. Another team also had promising results last year using a similar mechanism.

All of these studies, even if they don’t result in a vaccine in the next few years, provide scientists with vital information about how the immune system works. And who knows, maybe one day we’ll even be able to prevent the common cold!

Read more on our blog about germs and the immune system.