Swedish climate activist Greta Thunberg said Friday that she will not attend a United Nations climate conference planned for Glasgow in November due to the unequal supply of coronavirus vaccines, which is likely to hinder attendance from low-income countries.

“Of course I would love to attend the Glasgow #COP26,” the 18-year-old wrote on Twitter, referring to the 26th U.N. Climate Change Conference of the Parties, hosted this year by the United Kingdom. “But not unless everyone can take part on the same terms. Right now many countries are vaccinating healthy young people, often at the expense of risk groups and front line workers (mainly from global south, as usual …)."

She continued: “Inequality and climate injustice is already the heart of the climate crisis. If people can’t be vaccinated and travel to be represented equally that’s undemocratic and would worsen the problem.”

Thunberg’s comments are a blow for U.K. organizers, who due to the pandemic have already postponed the conference once from last November. Amid new surges in cases driven by variants, there has been speculation that it could be delayed again this year.

COP26 was slated to be the world’s most consequential climate conference since the 2015 Paris accord. On the agenda for discussion were country-level plans for cutting carbon emissions, as well as progress on the Paris agreement and the U.N. Framework Convention on Climate Change.

Some 20,000 people attended the last two conferences, and British organizers had initially hoped to bring 30,000 people to Glasgow, according to the BBC.

Thunberg, who has attended every other major climate conference in recent years, addressed the possibility of another postponement, writing on Twitter that global action should happen either way.

“If current trends continue and the #cop26 has to be delayed that doesn’t mean we have to delay the urgent action required,” she said. “We don’t have to wait for conferences nor anyone or anything else to dramatically start reducing our emissions.”

Thunberg first burst onto the global stage with a protest outside Sweden’s parliament 2 ½ years ago. She has since sparred with global leaders, notably President Donald Trump, and inspired a global, youth-led movement pushing for climate change solutions.

Along the way, she has continually kept the question of climate justice at the forefront of policy discussions.

“A digital solution is of course far from optimal,” Thunberg tweeted Friday, regarding the possibility that the conference could be partially or fully moved online. “High speed Internet connection and access to computers is extremely unequal in the world. In that case we would lack representation from those whose voices need to be heard the most when it comes to the climate crisis.”

While nearly 20 percent of people in the United States are now vaccinated, many other countries are unlikely to hit that target by the end of the year, even with international assistance through the Covax program. Based on current projections, it could be years before low-income countries distribute enough vaccines to come close to herd immunity, which scientists say requires inoculating some 70 to 80 percent of a population.

Since rollouts began late last year, enough vaccine doses have been distributed to fully vaccine about 5 percent of the world’s population, but the vast majority have been administered in wealthy and Western countries. Some 40 percent of vaccines have been given in 27 wealthy nations that include only 11 percent of the world’s population, according to the Bloomberg Vaccine Tracker.

While wealthy countries were able to pre-purchase vaccines, the unequal distribution means that many vulnerable populations in much of the world, such as health-care workers and the elderly, remain at high risk.

But scientists also warn that the longer the virus continues to circulate widely, the more chances it will have to change — and potentially develop vaccine resistance. Already, several highly contagious and dangerous variants are in circulation, driving new waves of infections and global disruption.

“Vaccine nationalism won’t solve the pandemic,” Thunberg wrote Friday on Twitter “Global problems need global solutions.”

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