The European Union will look for ways to end its vaccine struggles at a summit on Thursday, as a Covid-19 surge takes the death toll in Brazil past 300,000.

A crucial tool in the fight against the pandemic, vaccines were in the spotlight again with AstraZeneca revising down the efficacy of its shot from 79 to 76 percent after a US agency raised concerns about outdated numbers.

AstraZeneca's jab is also at the centre of the EU's vaccine woes, with an infuriated Brussels tightening export controls after the firm failed to deliver the doses it had promised to the bloc.

EU leaders will meet via videoconference on Thursday to discuss AstraZeneca supplies, as well as new vaccine export rules that will weigh how needy countries are in terms of infection rates, how many jabs they have, and how readily they export doses to the bloc.

‘Open roads should run in both directions,’ said European Commission chief Ursula von der Leyen.

Britain, which has raced ahead with its immunisation drive, is seen as one of the targets of the new export rules after a bitter spat over vaccine supplies.

UK Prime Minister Boris Johnson warned that the EU risked long-term damage to its reputation if it imposed ‘a blockade’.

The talks come as Germany, France, Belgium, Austria and the Netherlands tighten restrictions to control surges in cases.

Mass vaccination programmes are considered vital to ending the pandemic, which has claimed more than 2.7 million lives around the world, hammered the global economy and left much of humanity under punishing restrictions.

‘We were just waiting to be all together again because we were really sad to be divided like that, floor by floor,’ said Lydie, a 91-year-old resident of a retirement home in France's Val-de-Marne, where vaccinations have allowed an easing of curbs.

‘There was no joy. Now it's very good. We are happy.’

- 'Locked up' -Governments are trying to ramp up vaccinations, racing against the virus which is surging once again in many parts of the world.

Brazil's Covid-19 death toll passed 300,000 on Wednesday, the second-highest number of fatalities in the world, with its hospitals pushed to the brink.

At a demonstration in Rio de Janeiro marking 300,000 virus deaths in Brazil, protesters held signs that read ‘Shame’ and laid 30 roses on symbolic patient beds in front of a hospital.

Mexico, another hard-hit Latin American nation, neared 200,000 deaths, as authorities pressed on with a vaccination programme.

‘How have we spent (the pandemic)? Locked up,’ said Miguel Molina, 75, who got a jab in Mexico City.

‘I have (spent) a year and three months locked up, without going out. This is the first time I go out.

- 'Bump in the road' -The AstraZeneca shot was hailed as a breakthrough because it is cheaper and easier to store and transport compared with other vaccines.

But beyond production and supply issues, it has faced other challenges that have dented confidence.

AstraZeneca was forced to review its US trials and then slightly revise down the jab's efficacy from 79 percent to 76 percent, after an American agency raised concerns about outdated information.

Top US infectious disease expert Anthony Fauci had said the discrepancy was a ‘bump in the road’ and that data would show it is ‘a good vaccine’.

Where the EU vaccine rollout has stuttered, there has been huge progress in the United States -- the world's worst-hit nation.

Around 70 percent of Americans aged 65 or over -- more than 38 million people -- have received at least one dose, and hospital admissions for Covid-19 in that group are down 85 percent since early January.

But the pandemic threat is far from over, illustrated by the recent decision to bar overseas fans from the already delayed Tokyo Olympics.

The torch relay for the Games got off to a low-key start Thursday and organisers hope it will build excitement.

But Tetsuya Ozawa, among a small group of fans, told AFP it was not much fun without spectators.

‘There would have been more excitement if there wasn't coronavirus.’