Um I don’t know maybe because they aren’t God so they ain’t gonna know everything
The attenuated oral poliovirus vaccine (OVP) is no longer administered in the U.S.A. because it can be spread to contacts and can occasionally cause poliomyelitis.
<h3>What is Vaccine?</h3>
The vaccine may be defined as any substance which is prepared for the stimulation of antibodies and furnishes immunity against one or several diseases.
Oral poliovirus vaccines have chances to revert back into their wild-type strain and again cause disease. Children vaccinated with oral polio vaccines shed poliovirus which spread to contacts.
Therefore, it is well described above.
To learn more about Oral poliovirus vaccines, refer to the link:
brainly.com/question/7148795
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