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Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Hypertension is a silent killer because it is deadly and has no significant early symptoms. The danger from hypertension is the extra load on the heart, which can lead to hypertensive heart disease and kidney damage. This occurs without any major symptoms until the high blood pressure becomes extreme. Regular blood pressure checks are an important method of catching hypertension before it can kill you.
Approximately 500,000 babies are born each year in the United States to teenage mothers.
Pope Sylvester II tried to introduce Arabic numbers into Europe between the years 999 and 1003, but their use did not catch on for a few more centuries, and Roman numerals continued to be the primary number system.
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.