On a "pre-honeymoon" in Cabo San Lucas, Mexico, the pair are "wearing face masks everywhere we go. We're in isolation, we're in full hiding," Pratt told Ryan Seacrest on his KIIS-FM radio show Tuesday morning.
The couple, who held a wedding Saturday in California, went to Mexico for Montag to shoot a music video.
With the outbreak of the flu, which has so far killed 149 people in Mexico, the couple are being extra cautious. "Every second we're washing our hands," Montag told Seacrest.
The couple, who will star in I'm A Celebrity, Get Me Out Of Here this summer, plan to take a real honeymoon once the shoot is finished.
"Since it's a recession," said Pratt, "we just might go to Santa Monica Beach."