America's coronavirus death toll took a drastic turn for the worse this week as its number of fatalities surpassed the country's troop losses in World War II. New U.S. President Joe Biden is warning that the nation enters "what may well be the toughest and deadliest period of the virus.”

Coronavirus cases have surged past 96 million worldwide, fueled by the emergence of new variants including one that was first detected in Britain that has now spread to more than 60 nations, the World Health Organization (WHO) said Wednesday.

The United States remains the worst-hit country, with around a fifth of the 2 million global COVID-19 deaths, and Biden has made the fight against the pandemic his administration's top priority.

"We need all our strength to persevere through this dark winter. We're entering what may be the toughest and deadliest period of the virus," Biden said at his inauguration, where those in attendance wore face masks and social distancing was enforced.

A Johns Hopkins University tracker on Wednesday showed that 405,400 people have died from the disease, more than the 405,399 total U.S. combat and non-combat deaths in World War II.

Among the Biden administration's targets is the inoculation of 100 million Americans in 100 days, hoping to revive a vaccine rollout that had floundered in the last weeks of the Trump presidency.

E-commerce titan Amazon on Wednesday offered its vast logistics infrastructure to help with that effort. Biden's point-man for fighting the pandemic, Jeff Zients, said America would also rejoin the WHO, reversing his predecessor's decision. He added that top U.S. expert Anthony Fauci would lead a delegation to the WHO executive board meeting on Thursday.

The announcement came as the WHO confirmed that the virus variant first detected in Britain had spread to more than 60 countries, while one that emerged in South Africa has made it to 23.

The South African variant is more contagious than earlier ones, experts have warned. Both have tempered optimism that mass vaccination will help to end unpopular restrictions such as shutdowns that have wrecked economies around the world.

There was some good news, however, with early results from two studies on the Pfizer-BioNTech vaccine showing it is effective against the British variant, which is fuelling a surge that has overwhelmed U.K. hospitals.

"When you go into a hospital ... in some cases it looks like a war zone," the British government's chief scientist, Patrick Vallance, told Sky News. Britain is mounting a massive vaccination drive that has involved the repurposing of all kinds of large buildings including Salisbury Cathedral, where thousands of elderly people are receiving shots.

Two musicians worked in shifts throughout the day on its 19th-century organ, playing soothing pieces by composers including Bach and Dvorak. "It's quite a scary thing to be going through. The thought of the disease and what it can do to families and people," said Jeanie Grant, who had brought her 98-year-old father to the cathedral for his shot. "(So) to actually come to a building that has seen so much history and is still serving a beautiful purpose for the community, I think it's very special."

There are concerns, however, that rich nations are hogging doses. Of the 50 nations that have started vaccination campaigns, 40 are high-income, according to WHO assistant director-general Mariangela Simao, who also said efforts were underway to ensure access for all.

"No one needs to panic, because you're going to get a vaccine," she said. The WHO co-led COVAX facility, a globally-pooled vaccine procurement and distribution effort, has struck agreements with five manufacturers for 2 billion doses.

Interestingly, the urgency to be vaccinated wasn't being felt everywhere.

The Himalayan kingdom of Bhutan plans to vaccinate its entire population, but not until after March 13 because the period before has been deemed "inauspicious". The shots will start after that, the prime minister's office said, adding that it was "important we roll out the nationwide vaccination on an auspicious date."