As viewers, we have absolutely no clue how many clones there are living around the world, but it's assumed there are at least dozens. Helena killed off a few before the start of the series, and, between season one and tonight's season two premiere, BBC America released a short webisode following a never-before-seen clone named Jennifer Fitzsimmons. It's fashioned in the form of a video diary, showing Jennifer—looking totally healthy—explaining that she used to be a swim coach before she got sick.
Moments later, the video changes, and we see Jennifer in a hospital, bald and barely conscious. She's coughing up blood and conscious of the fact that she's dying. It's assumed that this is the same disease that Katja was dying from, and the one that Cosima has, making it all the more likely that other clones around the world are also susceptible to developing this illness.