This article attempts to summarize existing research on the accuracy of diagnosing apps (usually described as 'symptom checkers, SC). Given the novelty of shuch apps, the literature is neither large nor well-focused. And while it is at least all relatively recent, given the speed of app development, it is not clear it is recent enough.
To try and predict how useful AI may prove in healthcare, it is useful to first understand the types of problems were it may be helpful. There are a number of ways in which scientist and engineers can classify problems, but the four most important for this discussion
1) whether we have a good understanding of the problem (i.e., can we model it mathematically),
2) how many variables there are,
3) whether there is an underlying structure to the data, and
4) how much data we have on a given problem and it's quality.