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Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
There are 60,000 miles of blood vessels in every adult human.
About 3% of all pregnant women will give birth to twins, which is an increase in rate of nearly 60% since the early 1980s.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
There can actually be a 25-hour time difference between certain locations in the world. The International Date Line passes between the islands of Samoa and American Samoa. It is not a straight line, but "zig-zags" around various island chains. Therefore, Samoa and nearby islands have one date, while American Samoa and nearby islands are one day behind. Daylight saving time is used in some islands, but not in others—further shifting the hours out of sync with natural time.