The HIV virus can quickly adapt to escape the human immune system, which could present a challenge in designing one effective vaccine, new research suggests. In the study, published in the journal Nature, researchers looked at both the HIV genetic sequences and the immune system molecules that fight the virus in over 2,800 people in several countries, including Canada. HIV mutations that helped the virus fight off specific immune system genes were more prevalent in populations where those particular immune system genes were was also prevalent. “This is high speed evolution that we’re seeing in the space of just a couple of decades,” lead researcher Philip Goulder of the University of Oxford told the BBC. While it sounds like bad news, “it could equally be that as the virus changes, different immune responses come into play and are actually more effective,” he adds. “The implication is that once we have found an effective vaccine, it would need to be changed on a frequent basis to catch up with the evolving virus, much like we do today with the flu vaccine.”