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People who have myopia, or nearsightedness, are not able to see objects at a distance but only up close. It occurs when the cornea is either curved too steeply, the eye is too long, or both. This condition is progressive and worsens with time. More than 100 million people in the United States are nearsighted, but only 20% of those are born with the condition. Diet, eye exercise, drug therapy, and corrective lenses can all help manage nearsightedness.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Not getting enough sleep can greatly weaken the immune system. Lack of sleep makes you more likely to catch a cold, or more difficult to fight off an infection.
On average, the stomach produces 2 L of hydrochloric acid per day.
Blood is approximately twice as thick as water because of the cells and other components found in it.