Explanation
-People who are not immunized against a disease might still not - fall sick from the disease. If someone is trying to learn whether - or not preventative measures against the disease have any impact, - he or she might see these people and conclude, since they have - remained healthy despite not being immunized, that immunizations - have no effect. Consequently, he or she would tend to believe that - immunization (or other preventative measures) have fewer benefits - than they actually do.
-Explanation
+People who are not immunized against a disease might still not + fall sick from the disease. If someone is trying to learn whether + or not preventative measures against the disease have any impact, + he or she might see these people and conclude, since they have + remained healthy despite not being immunized, that immunizations + have no effect. Consequently, he or she would tend to believe that + immunization (or other preventative measures) have fewer benefits + than they actually do.
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