A 4-year-old child in Jerusalem tested positive for polio this week, marking the first known case of the virus in Israel since 1989.
The child was not vaccinated against the disease that causes paralysis in one out of every thousand people who are unvaccinated.
There are other likely asymptomatic cases as well, officials stated, and the virus has been found in sewage water samples.
"There are at least dozens or hundreds [of people in Israel infected with polio] who are apparently asymptomatic," warned Dr. Sharon, head of public health services at Israel's Ministry of Health.
"We do not expect a wave of children to show up with symptoms, but we understand that the virus is around," she said,according to Haaretz.
"A vaccinated child is a protected child," she added.
One Health Ministry official told Israel Hayom that hundreds or even thousands of children may have been exposed to the virus.
The child, whose family is also unvaccinated, is "in state of weakness and in a condition that could deteriorate to paralysis," the ministry source said, according to Israel Hayom.
The Ministry of Health is encouraging citizens to become fully vaccinated "with all due haste" in light of the outbreak.
Jerusalem's District Health office has started a contact tracing investigation and will make further recommendations dependent upon the findings of the inquiry, officials said.