I haven't been on this forum in ages. As far as I know (after doing some searches on this board,) this scenario is original.
It begins with the germs that cause pneumonia, and their deleterious effects on one Richard Feynman, who in OTL was a very brilliant physicist: discover of quantum electro-dynamics, popularizer of physics and the investigator into the O-rings that caused the Challenger shuttle disaster and its subsequent coverup.
The POD involves Feynman's time in Los Alamos during the Second World War, and involves a particularly pressing problem of communication between Los Alamos, where the atomic bomb was being designed, and the Oak Ridge facility in Tennessee, which was the facility where the fissionable uranium (U235) was being separated from its isotopes. (I won't give the technicalities here; you can find it in Feynman's book.) The point is, Oak Ridge didn't really know what they were doing with the stuff, and that if it were placed closely enough together, it would melt down or explode.
In OTL, it was Feynman who was sent to Oak Ridge, after the physicist Robert Christy contracted pneumonia. In this ATL, Feynman falls ill and Christy is sent to Oak Ridge. Christy is not given all of the calculations by Feynman due to his illness and, despite all of his attempts to convince them otherwise, is ignored by Oak Ridge--with catastrophic results...