The battle to subdue COVID-19 won’t be won until the whole world is vaccinated.

So President Biden’s virtual COVID-19 summit at the United Nations on Wednesday was an important step toward mobilizing wealthy nations to share far more doses and technology. It also laid bare the global divisions over fighting the pandemic, which aren’t just between the rich and the poor.

Seventy-nine percent of the shots in arms worldwide have been administered in high- and upper-middle-income countries and only 0.5 % in low-income countries. Less than 4% of Africa’s population is fully vaccinated, compared with 54% of Americans (a number that is high by comparison but painfully low in terms of where the United States should be).

For many Americans, especially the political anti-vaxxers, those global stats may seem irrelevant. But the truism “what goes around comes around” has never been more valid than with this novel virus.

» READ MORE: Much of the world struggles for vaccinations, while Americans refuse them | Trudy Rubin

“Vaccinating the world is a huge imperative. If we don’t, new variants will take over,” says Thomas Wright, coauthor of Aftershocks: Pandemic Politics and the End of the Old International Order. “This is a national security issue of the highest order, not just a question of generosity or foreign assistance. We are doing this for ourselves as well.”

That said, the summit displayed both the vital need for the United States to lead on the global vaccine effort and the enormous challenges for Biden.

The White House has now pledged to donate more than 1.1 billion doses to countries that need them, as well as to help expand production in several vaccine-manufacturing facilities across Africa and India that will be able to produce two billion doses for developing countries by 2022. It will also provide hundreds of millions of dollars for helping poorer countries get shots into arms and facilitate shipments of vaccines.

There were plenty of complaints after the summit from nongovernmental agencies that U.S. delivery has been too slow, and these numbers were insufficient. The World Health Organization estimates 11 billion does are needed globally to bring the pandemic under control.

And Biden’s goal of having 70% of the world’s population fully vaccinated by this time next year is clearly a pipe dream, however desirable. Yet it was clear at the summit that unless Washington takes the lead, there will be no global charge to corral this pandemic, or prevent the next one.

So Biden should be cheered on and pressed to deliver more, even if many public health organizations felt he fell short.

For one thing, the world is dangerously disunited about containing COVID-19. Neither Russia nor China took part in the Biden-led summit. And neither country is transparent about their own vaccine efforts.

Despite Xi Jinping’s pledge to provide the world this year with two billion doses of Chinese vaccines (whose effectiveness is questioned), Beijing has sold almost all the doses it has delivered to developing countries rather than donating them.

“We should unite around the world on a few principles,” Biden said at the summit: “That we commit to donating, not selling, doses to low- and lower-income countries, and that the donations come with no political strings attached.” That message was for China but will fall on deaf ears.

Moreover, the European Union has not delivered on its vaccine promises, and global health agencies have also faltered.

So the new emphasis should be — as Biden suggested — on developing manufacturing capacity for vaccines in middle- and lower-income countries. “We need to think how to diversify production and distribution facilities worldwide,” says Ezekiel Emanuel, vice provost for global initiatives at the University of Pennsylvania. “South Africa and Nigeria have capable people.”

This does not require big vaccine manufacturers to waive patent rights but can be done by voluntary licensing agreements that include sharing technologies and know-how. Johnson & Johnson, AstraZeneca, and Novavax had already signed such agreements last year with Indian manufacturers, and India was expected to power vaccine exports this year to poorer countries. But after botching its own vaccine program, the Indian government banned exports of vaccines.

Under U.S. and global pressure, India has pledged to begin exports again in October, which could help Biden’s international goals.

Yet the biggest threat to the global battle against COVID-19, as Biden well knows, may come from inside the United States.

The right-wing political hostility toward vaccines has undercut the White House’s ability to vaccinate the American public. So long as the battle over U.S. vaccinations continues — even as science now dictates boosters for elders and shots for kids — there are political limits on how much domestically produced vaccine Washington can donate abroad.

And so long as leading GOP figures scorn the need to promote shots – and vaccine mandates – the global battle to beat back this pandemic, or prevent the next one, is undermined.

Imagine if Florida’s Republican Gov. Ron DeSantis became president, let alone Trump redux, and left the next virus variant to rage unchallenged at home and abroad. Imagine if a GOP-controlled Congress refused to donate vaccines. No other country could fill the resulting leadership vacuum.

The battle to defeat COVID-19 globally starts right here at home.