Oral polio vaccines contain live viruses that can cause polio and are being replaced with a killed-virus version.
(Oral polio vaccines; contain; live viruses that can cause polio and are being replaced with a killed-virus version) (live viruses; can cause; polio) (live viruses; are being replaced; with a killed-virus version)
Oral polio vaccines live viruses live viruses
contain can cause are being replaced
live viruses that can cause polio and are being replaced with a killed-virus version
polio
with a killed-virus version