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