Pertussis vaccine people. With the acellular vaccines a brief period of non-serious swelling of the arm may occur. Side effects with both types of vaccines, but especially the whole-cell vaccine, are less common the younger the child. The whole-cell vaccines should not be used after seven years of age. Serious long term neurological problems are not associated with either type. The pertussis vaccine was developed in 1926. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. A version that also includes tetanus, diphtheria, polio, and Hib vaccine is available
Tay–Sachs disease Researchers are looking at gene therapy or enzyme replacement therapy as possible treatments. Tay–Sachs disease is typically first noticed in infants around 6 months old displaying an abnormally strong response to sudden noises or other stimuli, known as the "startle response". There may also be listlessness or muscle stiffness (hypertonia). The disease is classified into several forms, which are differentiated based on the onset age of neurological symptoms. Until the 1970s and 1980s, when the disease's molecular genetics became known, the juvenile and adult forms of the disease were not always recognized as variants of Tay–Sachs disease. Post-infantile Tay–Sachs was