The UK's former prime minister Tony Blair expressed concern that some countries could become "isolated from the world" because they lacked the capacity to vaccinate their populations.
Mr Blair called on the leaders of the wealthy G7 nations to redirect aid budgets to help poorer nations purchase Covid-19 vaccines.
He said the world would only reopen fully when a significant proportion of the global population was inoculated against the disease.
"China has been effectively shut down for a long period of time and will probably stay that way," he told London's Evening Standard.
“So they are able to control the disease inside their borders, and obviously it is a very powerful state in China, but if you’re going to open the world back up again, then you have got to make sure the entire world is vaccinated.
“And the big risk is that you end up with countries – and this is because we work so much with African governments – my anxiety is that you’re going to have countries essentially kind of isolated from the world, because they don’t have the capacity to vaccinate their people.”
Mr Blair challenged the G7 – Canada, France, Germany, Italy, Japan, the UK and the US – to unite the world to get vaccinated within eight months and to set up a global Covid variant tracking system.
“We should be doing everything we can,” he said.
Despair over UK foreign aid cut
The former prime minister's intervention comes as the UK's cut to its foreign aid budget – from 0.7 per cent to 0.5 per cent of national income – takes effect on a UN organisation that promotes sexual health.
The UN Population Fund (UNFPA) said on Thursday the cut meant the UK's commitment to the organisation would shrink from £154 million ($215m) this year to only £23 million.
"These cuts will be devastating for women and girls and their families across the world,” UNFPA's executive director Natalia Kanem said.
"With the now-withdrawn £130 million, the UNFPA Supplies Partnership would have helped prevent about 250,000 maternal and child deaths, 14.6 million unintended pregnancies and 4.3 million unsafe abortions."
Liz Sugg, a former foreign office minister who resigned in protest over the foreign aid reduction, said the cuts were a "double hit" on the world's poorest.
"The cuts which we're seeing to the aid budget are huge," she told the BBC's Radio 4 Today programme on Thursday.
“This is money the UK committed to in the UN chamber, signed an agreement and now we’re walking away from it – it’s pretty unheard of.”
Vaccines Minister Nadhim Zahawi emphasised the UK's commitment to the World Health Organisation's Covax initiative that helps supply vaccines to the world's poorest countries.
He said the UK had donated £548 million to the scheme.
“We are doing a hell of a lot to make sure we help the rest of the world,” he told Sky News.