JERUSALEM (JTA) — The wild polio virus was discovered for the first time in Jerusalem.

The virus, which was discovered several months ago in southern Israel and then spread to central and northern Israel, was discovered in Jerusalem’s wastewater treatment plant, Israel’s Health Ministry announced Monday.

Some 720,000 children ages nine and under have been vaccinated with a weakened form of the live virus in the last six weeks, slightly more than half of those being targeted for the extra vaccination. The children already have been inoculated against polio in their regular childhood vaccinations.

The purpose of the extra vaccine is to pass the weakened virus to adults with whom the children come into contact who may not previously have been vaccinated to allow their bodies to build up a resistance to the virus.

Across Israel, the vaccination rate against polio is 94 percent, according to the World Health Organization, which is supporting the vaccination campaign and whose representatives reportedly have called it “necessary.”

It is believed the virus was brought to Israel from Egypt; polio was discovered in sewage in Egypt in December. The same virus also is prevalent in Pakistan.

Israel experienced its last case of polio in 1988.