Iyad Abu El Hawa was arrested Thursday and will be held without bond at least until his Monday morning hearing, The Houston Chronicle reports.

Preliminary tests show the supposed vaccine was just water, the newspaper said, but authorities are urging those who got a shot to get tested for HIV and hepatitis C for their own safety.

El Hawa owns the Comfort & Caring Home Health clinic in Houston, and is accused of giving more than 1,600 fake flu shots.

The vast majority of those were administered to Exxon Mobil's Baytown employees, but a minority were nursing home patients on Medicare.

Exxon Mobil had contracted a private physician for the vaccinations, who then subcontracted with El Hawa, who does not have a medical license.

Exxon Mobil officials said this was the first time they outsourced the mass vaccinations. They usually hire staff to administer them.