A study by researchers at Tel Aviv University found that 70% of COVID-19 patients in Israel were infected by a strain that originated in the United States.

Scientists compared the genomic sequences of local patients to 4,700 genomic sequences taken from around the world, the Jerusalem Post reported.

The spread happened because Israel moved too late to bar people from the United States from entering the country, Adi Stern, professor in the School of Molecular Cell Biology and Biotechnology at Tel Aviv University, told The Post.

“There was this gap in policy, and this gap allowed people to return from the US who thought that they could go wherever they wanted, so they probably spread the virus that way,” Stern said.

Flights from other parts of the world into Israel were halted Feb. 26-March 4, but not flights from the United States, the Post said. Israel didn’t require people coming into the country to quarantine for 14 days until March 9, the Post said. Israel sealed its borders to all foreigners on March 18, the US Embassy in Israel said.

The other 30% of infections came from Europe, the Philippines, Australia, and Russia, the Post said, citing Stern.

Two other important findings, Stern said, were that transmission dropped sharply after the country locked down around March 20, and that 80% of cases were infected by 1-10% of the patients. Those “super-spreaders” may have infected people at parties or other large social events, she said.

Israel has had more than 16,000 coronavirus cases and 278 deaths, according to Johns Hopkins University. There have been 4.8 million cases worldwide with almost 322,000 deaths.