Israel will now vaccinate all children against polio as an attempt to eradicate the disease, the Health Minister Yael German explained.
German said 98 percent of Israelis were already vaccinated but could pass the virus onto the remainder.
"We discovered that we had several thousand temporary carriers of the virus," she told privately-owned Channel 2 television.
"It's only a matter of time, if we have thousands of carriers in the south -- our country is very small -- before the virus in the body of somebody who is innoculated meets somebody who is not, or whose immunity has weakened over the years," she said.
German said that children were the target group as they made up over 95 percent of those carrying the virus.
The health ministry last Monday launched a campaign to vaccinate 200,000 children up to nine years old in the south, where the virus showed up in routine tests at sewage treatment plants, but German said that a meeting of experts on Friday decided to go nationwide.
The ministry says 20,000 children have so far been vaccinated under the initial programme, which will be expanded from August 18.
The vaccine -- in the form of two drops administered orally on the tongue -- will be offered at children's health clinics.
German said nobody in Israel had been taken ill with polio since 1988 "and we are doing everything" to stop its return.