Early data indicates the Omicron Covid variant may more easily reinfect people who have already had the virus or been vaccinated than previous variants, but could also cause milder disease, the World Health Organisation (WHO) said.

“Emerging data from South Africa suggests increased risk of reinfection with Omicron,” WHO chief Tedros Adhanom Ghebreyesus told reporters, adding that “there is also some evidence that Omicron causes milder disease than Delta”.

But he stressed that more data was needed before drawing firm conclusions, and urged countries everywhere to boost their surveillance to help provide a clearer picture of how Omicron is behaving.

Even if it does turn out that Omicron causes less severe disease, Tedros warned against slacking off vigilance against the virus. “Any complacency now will cost lives,” he warned.

An adviser to British Prime Minister Boris Johnson resigned after footage of her joking about a Christmas party at Downing Street during lockdown last year aired on national television, reports AFP.

Allegra Stratton, formerly Johnson's press secretary and spokeswoman for the COP26 summit, tearfully said she would “regret those remarks for rest of my days” after the prime minister apologised and announced an internal probe over the video.

The leaked footage appears to contradict more than a week of denials by Johnson and his ministers that a party took place, following newspaper reports dozens of staff had attended an evening-long gathering on December 18, 2020.

The embattled leader faced calls for his resignation from some opposition politicians and vowed “disciplinary action” would be taken if the investigation found rules had been broken.

Global airlines blasted governments for worsening the Omicron scare through snap border measures and “rip-off” virus testing regimes, and urged politicians to let travellers make their own decisions based on scientific data.

Willie Walsh, director general of the International Air Transport Association, predicted “knee-jerk” border restrictions resulting from the coronavirus variant would ease soon, but it was too early to say whether holiday travel would be disrupted.

“We can't shut down everything when a new variant appears,” Walsh told a news briefing, adding hasty travel bans had penalised countries like South Africa for reporting findings.

Sindh has reported 176 coronavirus cases during the last 24 hours, according to a handout issued by the Chief Minister's Office. No new deaths were reported during this period.

According to the statement, 10,588 samples were tested during this period. The total number of cases has risen to 476,214 and the death toll remains 7,630.

Finland plans to make Covid-19 vaccines mandatory for health and social care workers, the government said.

The new legislation would also allow social and health care employers to access information about employees' Covid-19 vaccinations and possible infections in the past, Minister of Family Affairs and Social Services Krista Kiuru told a news conference.

Britain has urged private Covid-19 test firms to stop exploiting travellers, after a former competitions chief said the market was a “rip-off jungle”, reports AFP.

“We've been clear it is unacceptable for any private testing company to take advantage of holidaymakers," the Department of Health and Social Care said in a statement. “The government has taken action to drive down the cost of tests for international travel.”

Earlier, Lord Andrew Tyrie, former chairperson of the Competition and Markets Authority, labelled the Covid-19 tests market a “rip off jungle”.

Tyrie told BBC that “misleading online advertisements, overpricing [and] unacceptably poor service ... are still widespread” in the market. “To allow this to continue over the peak Christmas period would be scandalous,” he warned.

Omicron is spreading faster than any other coronavirus variant seen so far, Reuters quotes Prime Minister Boris Johnson as saying as he urged people to get booster vaccines.

“We now have, in the Omicron variant, a variant that is spreading much faster than any variant that we've seen before and that is what we need... to focus on,” Johnson told lawmakers.

“That is why I ask everybody to go and get their booster jab as soon as they're called forward.”

Countries considering introducing vaccine mandates in the fight against Covid-19 must ensure they respect human rights, the UN rights chief said, stressing that forced vaccination was never acceptable.

Speaking to a Human Rights Council seminar via video message, Michelle Bachelet warned there were significant rights considerations that needed to be taken into account before making vaccination compulsory, AFP reports.

Any “vaccine mandates must comply with the principles of legality, necessity, proportionality and non-discrimination”, she said, according to a transcript. “In no circumstances should people be forcibly administered a vaccine.”

BioNTech and Pfizer said a three-shot course of their Covid-19 vaccine was shown to generate a neutralising effect against the new Omicron variant in a laboratory test.

In the first official statement from vaccine manufacturers on the likely efficacy of their shot against Omicron, BioNTech and Pfizer said in a joint statement that two vaccine doses resulted in significantly lower neutralising antibodies but that a third dose of their vaccine increased the neutralising antibodies by a factor of 25.

They added that, if needed, they can deliver an Omicron-based vaccine in March 2022.