"30% were placebos" is actually not the main message I would take from this chart. Under-reporting in certain areas/times is certainly a possibility, as is the possibility that some lots would be less reactogenic than others (possibly due to poor quality control or poor handling).

The message that I would shout is about the blue line. Why is it that the worst batches were given to the fewest people? To me this says that someone was paying attention and stopping injection of those lots based on real-time reporting but was keeping that information quiet.