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Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
Many medications that are used to treat infertility are injected subcutaneously. This is easy to do using the anterior abdomen as the site of injection but avoiding the area directly around the belly button.
The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."
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.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.