Vaccines lack rational design. They are made using trial and error with no understanding of the mechanisms. The result is poor quality vaccines that are ineffective and cause disastrous adverse events. Sanofi Pasteur's Dengvaxia is the latest example. Children who received Dengvaxia experienced a higher risk of hospitalization due to a dengue infection. Before that it was Glaxo Smith Kline's Pandemrix vaccine that resulted in the narcolepsy disaster. Vaccine designers designing new vaccines are in no hurry to change. They are making new vaccines without understanding why the Dengvaxia vaccine failed. Thus assuring more disasters to come.