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Before a vaccine is licensed in the USA, the Food and Drug Administration (FDA) reviews it for safety and effectiveness. The CDC then reviews all studies again, as well as the American Academy of Pediatrics and the American Academy of Family Physicians. Every lot of vaccine is tested before administration to the public, and the FDA regularly inspects vaccine manufacturers' facilities.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
On average, the stomach produces 2 L of hydrochloric acid per day.
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."