Sometimes people who just happen to be near a clinic at closing time are offered leftover shots that would otherwise be thrown away. Sometimes health workers go out looking for recipients. Some places keep waiting lists and draw names at random. Such opportunities may be becoming more prized as shortages around the U.S. lead some places to cancel vaccinations.

“One of the nurses said I should go buy a lottery ticket right now,” said Jesse Robinson, outside a Nashville, Tennessee, clinic this week where the 22-year-old was picked from a 15,000-name list for a shot. “I’m not going to question it too much. Just glad it was me.”

David MacMillan was grabbing ingredients for a coconut chickpea dish at a Giant grocery store in Washington when a woman in a lab coat from the in-store pharmacy came up to him and his friend.

“I got two doses of the Moderna vaccine. The pharmacy is closing in 10 minutes. Do you want them?” MacMillan, 31, recalled the woman saying. “I thought, ‘Let’s go for it.’”