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Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
Common abbreviations that cause medication errors include U (unit), mg (milligram), QD (every day), SC (subcutaneous), TIW (three times per week), D/C (discharge or discontinue), HS (at bedtime or "hours of sleep"), cc (cubic centimeters), and AU (each ear).
Blood is approximately twice as thick as water because of the cells and other components found in it.
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.
Vaccines prevent between 2.5 and 4 million deaths every year.