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Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Asthma is the most common chronic childhood disease in the world. Most children who develop asthma have symptoms before they are 5 years old.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
For about 100 years, scientists thought that peptic ulcers were caused by stress, spicy food, and alcohol. Later, researchers added stomach acid to the list of causes and began treating ulcers with antacids. Now it is known that peptic ulcers are predominantly caused by Helicobacter pylori, a spiral-shaped bacterium that normally exist in the stomach.
The Romans did not use numerals to indicate fractions but instead used words to indicate parts of a whole.