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There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Acetaminophen (Tylenol) in overdose can seriously damage the liver. It should never be taken by people who use alcohol heavily; it can result in severe liver damage and even a condition requiring a liver transplant.
A seasonal flu vaccine is the best way to reduce the chances you will get seasonal influenza and spread it to others.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.