Do vaccine lotteries work?

Wharton’s Katy Milkman shares the lessons learned from last year’s Philly Vax Sweepstakes, a Penn-funded project designed to evaluate ways of increasing COVID-19 vaccinations in the city.

There were high hopes last year when Penn researchers and Philadelphia policymakers launched the Philly Vax Sweepstakes, a project designed to increase COVID-19 vaccinations by randomly awarding cash prizes to some residents who got the shot.

But the carefully designed, six-week program yielded mixed results. While the overall sweepstakes may have generated extra vaccinations in Philadelphia, its test of targeting specific zip codes with higher odds of a win definitely didn’t work.

gloved hand holding covid vacciine

Katy Milkman, a Wharton School professor and co-director of the Behavior Change For Good Initiative (BCFG) at Penn, is the lead author of the study published in the journal Nature Human Behavior. A team of scientists at BCFG partnered with city officials to design and fund the sweepstakes, which was unique from other vaccine incentive programs that were rolling out across the country in 2021. Instead of winning free food, scholarships, gift cards, and other items, Philadelphia residents were treated to a “regret lottery” in which they were automatically entered if they lived in the city (whether or not they’d been vaccinated). They were then contacted if their name was selected and could win up to $50,000, but only if they could prove that they’d taken the shot before the drawing.

The university and the city worked to spread the news about the Philly Vax Sweepstakes through local media and social networks, with a clear message that residents of three particular randomly selected ZIP codes (one picked every two weeks) would have a 50 to 100 times greater chance than other Philadelphians of winning cash. The researchers randomly chose these three ZIP codes from among 20 with the lowest vaccination rates in the city, hoping the boost would incentivize more residents in those ZIP codes to get vaccinated. But the bigger grab at cash did nothing.

“We got an incredibly clear answer: No. It was totally useless to multiply the chances by 50 to 100 of residents in certain ZIP codes winning. We do not see a benefit of that,” Milkman says.

The controlled part of the experiment didn’t produce even one extra vaccine for every $5,000 spent. The researchers confidently ruled out any benefit. Milkman said the result is still useful because it shows that geo-targeting, which seems like a sound idea, should not be considered as a way to motivate people.

Milkman adds there may still be overall value that can be extracted from vaccine regret lotteries, and believes more research is warranted.

Read more at Knowledge at Wharton.