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Vaccines prevent between 2.5 and 4 million deaths every year.
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.
Since 1988, the CDC has reported a 99% reduction in bacterial meningitis caused by Haemophilus influenzae, due to the introduction of the vaccine against it.
Vampire bats have a natural anticoagulant in their saliva that permits continuous bleeding after they painlessly open a wound with their incisors. This capillary blood does not cause any significant blood loss to their victims.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.