Over the course of history, viruses have caused hundreds of millions of deaths (literally). For example, in 1967 alone, the World Health Organization estimates that small pox killed an estimated 2 million people worldwide. And keep in mind, this is just one virus over the course of one year. Ultimately, the total number of people killed by viruses is simply staggering. Stopping the viruses is a terribly complex process; however, the basic way that many of them survive in humans is rather simple. In short: Viruses are unable to make proteins on their own. As a result, they overtake our proteins in order to subsist. Without the proteins, they could not sustain themselves. This, as it turns out, is fantastic news for one pair of siblings.
A brother and sister have an incredibly rare genetic disorder that causes them to have "broken" proteins. This makes them immune to many classes of viruses. Of course, the proteins aren't really "broken" per se. Rather, this genetic mutation alters a biological process called glycosylation (when a sugar molecule is attached to something else, like a protein). These resulting sugar-proteins are used by many viruses to build protective shells. In the children, this condition causes their bodies to stop viruses from building these protective shells.
This leaves the viruses "naked" and vulnerable, researchers report in the New England Journal of Medicine, which suggests new possibilities for antiviral treatments.
Ultimately, if they are unable to build a protective shell, many viruses are stopped in their tracks, including influenza, herpes, dengue fever, hepatitis C, HIV, and so on. Of course, there are some exceptions, like adenoviruses aka the common cold. Still, having protection from so many other viruses is an incalculable advantage.
However, like most people with genetic conditions, there are some side effects. The siblings noted here have suffered developmental delays, hearing loss, fragile bones, and a weakened immune system. Yet, despite these factors, they rarely got ear infections or the flu. Moreover, an antiviral treatment developed using the basic premise of this genetic condition could block glycosylation only temporarily, which would prevent viral infection without the devastating side effects. In fact, one such drug is being tested on individuals with HIV, and so far the treatment looks promising. "The worst side-effect was flatulence," Dr. Sergio Rosenzweig told NBC News. Although a reliable way to prevent viral infections is still a ways off, this condition could hold the secret to the "cure."