So now that H7N9 has been around for roughly a year, we have a chance to measure its functional rate of infectability using China's history of H5N1 detections vs the current level of H7N9 detections. Churning through those numbers, we conservatively calculate that H7N9 is 61 more times infective H5N1.
To make the comparison as apples to apples as possible, we limited H5N1's detection period to the post SARs timeframe when China's enhanced surveillance for Pneumonias of Unknown Etiology (PUE) took effect.
From 2005 through 2014, during a 98 month period China detected 44 H5N1 cases.
From Feb 2013 through Feb 2014, during a nearly 12 month period China detected 330 H7N9 cases.
Ratioing the relative monthly infection rates, H7N9 comes out as 61 times as infective.
Frankly, H7N9 doesn't becoming immediately concerning to us until it becomes at least 1000 times more infective than H5N1. As it stands now, what has happened with H7N9 may have happened many, many times before, but went undetected because there was no PUE surveillance.
If the Chinese are even moderately forth coming with information, by May we should know if H7N9 is exponentially more infectious than H5N1. Our government expects that it will be.