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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.
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
The most common childhood diseases include croup, chickenpox, ear infections, flu, pneumonia, ringworm, respiratory syncytial virus, scabies, head lice, and asthma.
Blood is approximately twice as thick as water because of the cells and other components found in it.