“We found no image boost for the U.S. — but we found something deeper: generosity triggering more generosity.”
— Changkeun Lee

Can generosity spread from country to country like a contagion?

In 2021, South Korea was running out of vaccines. The country had managed the first waves of Covid-19 remarkably well, but that early success came with a downside: it delayed the urgency of securing vaccine contracts. As a result, millions of younger Koreans were left wondering when — or if — they’d get their first shot.

Then came an unexpected move: the United States donated over 1.4 million Johnson & Johnson vaccines to South Korea. It was part of a broader American effort to supply vaccines globally — a gesture of goodwill that some policymakers hoped would also restore the country’s global standing.

But did it work? Did South Koreans, grateful for the American jabs, come to view the United States more positively?

A new study says: not quite.

“We found no meaningful shift in favorability toward the U.S.,” says Changkeun Lee, one of the study’s authors. “But we did find something arguably more important: people who received donated vaccines were more willing to help others.”

This “pay it forward” effect is at the heart of a new paper that explores how foreign aid — even when it doesn’t change opinions of the donor — can plant the seeds of international cooperation.

The limits of vaccine diplomacy

Previous theories of soft power suggest that acts of generosity can improve a country’s reputation. And vaccines — lifesaving, tangible, and visible — seemed like the perfect diplomatic tool.

Yet when Lee surveyed South Koreans before and after vaccination, they found no consistent evidence that U.S.-produced vaccines improved views of the U.S., whether the shots were donated or purchased. Even those who correctly identified the national origin of their vaccine didn’t view the U.S. more favorably.

That might seem disappointing — but the story doesn’t end there.

The surprising second-order effect

When the researchers looked at people who received donated vaccines, something unusual appeared: those recipients were significantly more likely to support South Korea donating vaccines to other countries in need. They didn’t express gratitude toward the U.S. — but they were more willing to pass the goodwill on.

And this wasn’t a matter of political leaning. The effect held even when controlling for ideology. In fact, a separate experiment found that simply telling people the U.S. was giving vaccines to developing countries made moderates — the largest ideological group — more supportive of South Korea doing the same.

“What matters isn’t just who gives, but how giving shapes what others do,” Lee explains. “This is about generalized reciprocity, not public relations.”

How the researchers tested it

To measure these effects, the researchers conducted a two-wave panel survey in South Korea in 2021 and 2022 — one during vaccine scarcity, and the other after most people had been vaccinated.

They used a difference-in-differences approach to track how individuals’ views changed before and after they got vaccinated. But to isolate the effects of donated vaccines, they relied on a unique policy quirk: because of concerns about blood clot risks, South Korea limited eligibility for the donated Johnson & Johnson (J&J) vaccines to people aged 30 and older.

This age-based eligibility rule created a natural cutoff. By comparing people just above and just below age 30, the researchers could estimate the causal impact of receiving U.S. vaccine aid — a technique known as regression discontinuity.

They also embedded an information experiment in the second survey wave. A random subset of respondents were told that the U.S. was donating vaccines to developing countries. This allowed the researchers to test whether simply knowing about U.S. aid changed people’s support for Korean foreign aid — even if they hadn’t received any foreign vaccines themselves.

Crucially, the team confirmed that most respondents correctly identified the country of origin of their vaccine, ruling out confusion as an explanation for the null results on U.S. favorability.

What it means for future aid

The results offer a more complex — and perhaps more hopeful — picture of what foreign aid can achieve. The authors argue that aid should not be judged solely on whether it enhances the donor’s popularity. Instead, we should ask: does it inspire further cooperation?

In a pandemic, where delay costs lives, the ability of one act of generosity to trigger another could be a more powerful form of influence than any soft power metric.

In policy terms, this suggests prioritizing aid recipients with the capacity to "pay it forward" — whether through surplus vaccine production or strong logistical systems — may help foster chains of cooperation. And it means communication about aid efforts matters too: visibility, not just volume, shapes public opinion.

About the Paper

Title: Paying It Forward: Vaccine Provision and Generalized Reciprocity in Foreign Policy Opinion
Authors: Changkeun Lee and Joonbum Bae (Colorado State University, former KDIS professor)
Publication: forthcoming at Public Opinion Quarterly
Data: Two-wave panel survey (2021–2022) of South Korean adults, with embedded randomized experiments
Design Highlights: Difference-in-differences estimation, regression discontinuity around age 30 for donated J&J vaccines, and information treatment experiment on vaccine aid