Brazil hit the grim mark of half a million COVID-19 deaths Saturday, a toll second only to the U.S. that shows few signs of easing. Yet residents are spurning vaccines that they believe are substandard in favor of hard-to-find shots from Pfizer Inc.

In Sao Paulo, people demand the U.S. company’s shots at public clinics and often walk out if none are available. Some health care centers have put up signs saying "no Pfizer shots” to save time. Many vaccination centers are empty, and the few that have Pfizer have massive lines.

Maressa Tavares, a 29-year-old teacher, could have gotten her shot two weeks ago in Rio de Janeiro. But at the request of her father, she’s holding out for Pfizer. "For me, it didn’t make a lot of difference which one to take, but my father has very strong beliefs,” she said.