World Health Organization experts on Wednesday inspected a Chinese laboratory in Wuhan that some US officials said could have been the source of the coronavirus, as global vaccine hopes rose with strong results reported for Russia's Sputnik V jab.

The Covid-19 pandemic has shown no signs of slowing down even as vaccines are rolled out, with known infections surging past 103 million, more than 2.2 million dead and the global economy devastated.

A WHO team searching for clues about the pandemic's origins went to the Wuhan Institute of Virology, one of the most-watched stops on a politically sensitive trip to the central Chinese city where the virus was first detected.

Peter Daszak, one of the experts, said the team was "looking forward to a very productive day and to asking all the questions that we know need to be asked".

But top WHO officials, including members of the team, have played down the chances of finding any definitive answers on this trip, including how the virus jumped from animals to humans.

"It is very unlikely that (on) such a short mission, (we) would have a very advanced understanding or definite answers" about the origins of the virus, WHO team member Hung Nguyen-Viet told AFP from Wuhan.

The trip is under intense scrutiny, following months of calls led by the United States for an independent, transparent probe into how the disease exploded into a once-in-a-century pandemic.

One of the theories circulated in the early days of the pandemic -- and being pushed by people including then-president Donald Trump and some officials in his administration -- was that the virus had leaked from the high-security lab in Wuhan, though there has been no evidence to back it up.

Sputnik V boost

As the WHO team probed the origins of the pandemic, hopes for ending it were boosted by the publication of final-stage trial results from Russia's Sputnik V vaccine that showed it was 91.6 percent effective against symptomatic Covid-19 cases.

Russia and several other countries had rolled out the vaccine last year, with scepticism about its quality and concerns that it had been rushed without conclusive testing.

But the results published in The Lancet, a leading medical journal, put it at par with Western-developed vaccines such as the ones from Pfizer-BioNTech and Moderna.

Mexico on Tuesday became the latest nation to approve the Russian vaccine -- named after the world's first artificial satellite.

It had already been authorised by more than 15 countries, while German Chancellor Angela Merkel said "every vaccine is welcome in the European Union", citing the "good data" for the Russian vaccine.

Sputnik V has the advantage of being relatively cheap and it can be stored at normal refrigerator temperatures, unlike the special, below-freezing storage required for the Pfizer and Moderna shots.

That could be a major boost for vaccination efforts in the less wealthy parts of the world.

More than 100 million vaccinations have been carried out worldwide, but none of the world's 29 poorest countries has formally started mass inoculations.

Despite infighting over deliveries and stuttering rollouts, the richest nations have dominated available supplies.

President Emmanuel Macron said Tuesday that all people in France who want a vaccine would be offered one "by the end of the summer".

Meanwhile in the impoverished Palestinian Territories, health workers on Tuesday started receiving shots sent by Israel, which had faced a pressure campaign to help people in occupied areas access vaccines.

Non-stop mourning

The threat of the pandemic came into sharp focus as Latin America and the Caribbean logged more than 600,000 Covid-19 deaths on Tuesday, the second-highest number of virus fatalities after Europe.

Brazil and Mexico account for about half the deaths in the region, which have overwhelmed infrastructure, including cemeteries.

"What do you say to these people? There are no words, no words to give them some relief in the face of such loss," said Margarita Beristain Villa of the Jardines del Recuerdo cemetery in Mexico.

"There are families that have lost various relatives, it's a non-stop mourning process."

Meanwhile in Britain, tributes flooded in following the death of Captain Sir Tom Moore, the 100-year-old military veteran who won hearts by raising nearly 33 million pounds ($45 million) for UK health service charities.