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Between 1999 and 2012, American adults with high total cholesterol decreased from 18.3% to 12.9%
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Giardia is one of the most common intestinal parasites worldwide, and infects up to 20% of the world population, mostly in poorer countries with inadequate sanitation. Infections are most common in children, though chronic Giardia is more common in adults.
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.
Intradermal injections are somewhat difficult to correctly administer because the skin layers are so thin that it is easy to accidentally punch through to the deeper subcutaneous layer.