The original probability at week zero was 29% and the current probability is 79%.  That means that the probability has increased by 172% (79% / 29% - 1).  

However, it is accurate to say that the probability has increased by 50 percentage points.

Real world example of everyday importance of this.  When interest rates increase from 4% to 6%, that is not a 2% increase in the increase rate, it is a 50% increase in the interest rate, and the reason why so many people cannot afford homes right now.  The rate has gone up by 2 percentage points, but that reflects a 50% increase in the rate.