Millions of Americans defied Covid-19 guidelines Thursday to spend a subdued Thanksgiving holiday with family and friends, while questions emerged over the level of protection that one potential vaccine offers.

About a million people were screened at US airports each day over the last week, as many appeared bent on enjoying one of the country's biggest annual celebrations.

IMAGES AND SOUNDBITESDespite the Covid-19 pandemic, the Los Angeles Mission maintains it's annual food distribution to help nourish those struggling to make ends meet this Thanksgiving. "A hot meal, it warms your heart," says one beneficary. IMAGES AND SOUNDBITESDespite the Covid-19 pandemic, the Los Angeles Mission maintains it's annual food distribution to help nourish those struggling to make ends meet this Thanksgiving. "A hot meal, it warms your heart," says one beneficary. Photo: AFPTV / Romain Raynaldy

The exodus came despite warnings that mass travel threatens to significantly worsen the pandemic in the country hit hardest, with a six-month high of more than 2,400 deaths registered in the US in just the past 24 hours.

President-elect Joe Biden offered a message of hope, however, in a Thanksgiving video address that rallied Americans to pull together to defeat the outbreak.

Skiers wearing protective face masks against the spread of the Covid-19 hit the slopes in the Swiss Alpine ski resort of Verbier on November 15, 2020 Skiers wearing protective face masks against the spread of the Covid-19 hit the slopes in the Swiss Alpine ski resort of Verbier on November 15, 2020 Photo: AFP / Fabrice COFFRINI

"I know better days are coming, I know how bright our future is. I know the 21st Century is going to be an American century," he said.

British pharmaceutical giant AstraZeneca, one of three firms that have reported their vaccine to be ready, said Thursday that further research was needed after questions emerged over the protection it offers.

Change in the percentage of case numbers recorded during 7 days compared to the previous 7 days, for countries which have more than 1,000 daily cases. Change in the percentage of case numbers recorded during 7 days compared to the previous 7 days, for countries which have more than 1,000 daily cases. Photo: AFP / Romain ALLIMANT

The manufacturer initially said its vaccine was 70 percent effective, and then said it was 90 percent effective when an initial half-dose and then a full dose were given.

But US scientists said the higher rate came during tests in people aged 55 and under.

US President-elect Joe Biden arrives to deliver a Thanksgiving address at the Queen Theatre in Wilmington, Delaware, on November 25, 2020, where he tried to rally Americans weary of the Covid-19 pandemic US President-elect Joe Biden arrives to deliver a Thanksgiving address at the Queen Theatre in Wilmington, Delaware, on November 25, 2020, where he tried to rally Americans weary of the Covid-19 pandemic Photo: AFP / CHANDAN KHANNA

Vaccine breakthroughs have raised hopes for an end to the outbreak, though much of the world faces a gloomy winter dampened by lockdowns, economic anxiety and devastating loss.

Anthony Fauci, the top US infectious disease expert, said he was expecting "a surge superimposed upon a surge" caused by the big holiday getaway.

A woman wearing a face mask walks down a street in central Moscow on November 25, 2020, as cases continue to climb globally A woman wearing a face mask walks down a street in central Moscow on November 25, 2020, as cases continue to climb globally Photo: AFP / Dimitar DILKOFF

President Donald Trump, for his part, spent the day golfing at a course he owns in Virginia, taking time out to attack Biden's record-setting winning vote count in the election earlier this month.

"Just saw the vote tabulations. There is NO WAY Biden got more than 80,000,000 votes!!! This was a 100% RIGGED ELECTION," he fumed on Twitter.

Passengers check in at Los Angeles International Airport ahead of Thanksgiving in Los Angeles, California, November 25, 2020, after US health authorities urged Americans not to travel for the annual holiday Passengers check in at Los Angeles International Airport ahead of Thanksgiving in Los Angeles, California, November 25, 2020, after US health authorities urged Americans not to travel for the annual holiday Photo: AFP / Patrick T. Fallon

Globally, more than 60 million infections and 1.4 million deaths have been recorded since the new coronavirus emerged in China late last year, according to a tally compiled by AFP from official sources.

US Vice President-elect Kamala Harris and her husband Doug Emhoff visit a food bank in Washington, DC on November 25, 2020, ahead of the Thanksgiving holiday US Vice President-elect Kamala Harris and her husband Doug Emhoff visit a food bank in Washington, DC on November 25, 2020, ahead of the Thanksgiving holiday Photo: AFP / SAUL LOEB

Despite the burst of travel in America -- still far below last year's Thanksgiving numbers -- pandemic restrictions meant that there was a resolute, stoical undercurrent to this year's festivities.

The Macy's Thanksgiving Day Parade in New York, a cherished tradition nearly a century old featuring giant balloons and colorful floats, went ahead in a truncated made-for-TV celebration across just one city block, with no crowds and much of it pre-recorded.

Despite the Covid-19 pandemic, the Los Angeles Mission maintains it's annual food distribution to help nourish those struggling to make ends meet this Thanksgiving. "A hot meal, it warms your heart," says one beneficary. Despite the Covid-19 pandemic, the Los Angeles Mission maintains it's annual food distribution to help nourish those struggling to make ends meet this Thanksgiving. "A hot meal, it warms your heart," says one beneficary. Photo: AFPTV / Romain Raynaldy

Biden described how he normally travels to the New England coast for a big family feast but would be staying home in Delaware this year for a small get-together.

"I know this isn't the way many of us hoped we'd spend our holiday. We know that a small act of staying home is a gift to our fellow Americans," he said in his video message, posted to social media.

On radio and TV, chefs have been making suggestions on scaling down meals for smaller gatherings, or even sharing bits of what they cook and leaving it on the doorstep of friends and family, so it at least feels like a shared meal.

The New York Times asked readers to state in six words or fewer what they were grateful for and published some of these lines, as Americans tried to make the best of the holiday.

"A furtive hug with a friend," one entry reads.

"Windows have never been so important," said another.

America's political divisions were also evident.

Trump's White House has urged "all Americans to gather, in homes and places of worship," despite the health risk.

But Biden has been calling on people to hunker down and keep observing health guidelines until a vaccine becomes available.

While low-income frontline workers often face the biggest risks from the virus, it has also run rampant among the world's wealthiest and most powerful.

On Thursday, Sweden's Prince Carl Philip and his wife Princess Sofia went into self-isolation after testing positive for Covid-19, the palace said.

With Britain and France talking about easing their lockdown measures soon, Russia is still resisting stay-at-home orders despite registering record infections and deaths from the virus Thursday.

Countries that have had strong success against the virus are also cracking down on new outbreaks.

South Korea closed bars and nightclubs this week as it braces for a third major wave, with virus cases at their highest level since March.

"The exceptions have been some governments that shrugged off the painful evidence of mounting deaths, with inevitable, grievous consequences. But most governments acted responsibly, imposing strict measures to contain the outbreak."