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Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
In inpatient settings, adverse drug events account for an estimated one in three of all hospital adverse events. They affect approximately 2 million hospital stays every year, and prolong hospital stays by between one and five days.
Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
Autoimmune diseases occur when the immune system destroys its own healthy tissues. When this occurs, white blood cells cannot distinguish between pathogens and normal cells.