It's been another volatile session for markets in the U.S. and Europe as shareholder activists continue their campaign against hedge funds, short selling stock for profit. At one point, online brokerage firms including Robinhood stopped selling new positions in the most heavily traded firms like that of troubled video games retailer GameStop. Now the affair has come to the attention of regulators, lawmakers and even Elon Musk. 

Elsewhere, vaccination programs across the EU continue to be dealt a blow by pharma firms, with Moderna becoming the latest to warn of fewer doses than expected being delivered next month. 

However, there is good news from one group – Novavax trials showed a 90 percent efficacy rate for its new COVID-19 treatment.

Online retailers including Boohoo continue to target some of the best-known names of the UK high street that have buckled under the weight of lockdown trading conditions. 

While the latest figures show the debt impact of the pandemic may be with us long after COVID-19 is finally brought under control.

Read on for more of the days business news.

Louise Greenwood

Digital business correspondent 

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Market regulators have warned they are keeping a close eye on amateur traders after a volatile session on Thursday caused brokers to temporarily restrict access to stocks targeted by groups on social media. 

Share prices in companies, most notably video games retailer GameStop, have spiked after being singled out by activist groups on trading platforms such as Robinhood and Interactive Brokers. 

The U.S. clearing house the Depository Trust and Clearing Corporation (DTCC) has warned of the "substantial risk exposures at firms that clear these trades", while the UK's Financial Conduct Authority told amateur traders to "ensure they are familiar with all regulations, including market abuse."

Shareholder groups, many using mobile phone apps, have targeted stock they feel is being unfairly short-sold by top hedge funds in a battle that has caused alarm on Wall Street and even in Congress. 

Tesla boss, Elon Musk is among those who have hit out at the institutional short-sellers seeking to profit from the trading difficulties that many firms like GameStop are experiencing in the pandemic slowdown. In a tweet, Musk stated: "u can't sell houses u don't own, u can't sell cars u don't own, but u *can* sell stock u don't own!? … shorting is a scam legal only for vestigial reasons."

Pharma giant Moderna has told Italy and France it will deliver fewer doses than expected next month. France's Ministry of Health now says it believes up to 25 percent fewer treatments than hoped may arrive, in another blow to struggling vaccination campaigns across EU states. It comes after rival drugs firm AstraZeneca warned EU officials last week that less than half of the vaccines ordered may be delivered in the first three months of the year.

Meanwhile, a leading European business group has warned EU plans to allow member states to block vaccine exports could have a "devastating" effect on supplies. In a letter to European Commission President Ursula von der Leyen, the Paris-based International Chamber of Commerce said the move to limit exports could quickly backfire, and "very rapidly erode essential supply chains." 

However, shares in US-based Novavax jumped 26 percent in late trading on Thursday after trials showed its new COVID-19 treatment to be nearly 90 percent effective against variants of the virus first discovered in the UK and South Africa. The trial results could soon put the vaccine on a path to authorization in multiple countries. 

Profits at U.S. drugmaker Eli Lily rose 41 percent in the fourth-quarter of last year, boosted by demand for its diabetes drugs as well as the successful launch of its COVID-19 treatment. The Indianapolis-based firm posted worldwide revenues of $871 million for the three months to the end of 2020, with its Bamlanivimab antibody therapy found to significantly reduce COVID-19-related hospitalizations.

Online fashion retailer Boohoo says it is in "exclusive" talks with the failing UK retail group Arcadia to buy key parts of its business. Arcadia, owned by Philip Green, fell into administration last November, putting 13,000 store jobs at risk. Boohoo is said to be interested in purchasing the Dorothy Perkins, Wallis and Burton brands, but not the bricks-and-mortar premises. Its rival Asos is also in talks with Arcadia over a buyout of its Topshop, Topman and Miss Selfridge labels.

U.S. consumer spending fell in December for the second month in a row, but not by as much as analysts had feared. Overall spending was down 0.2 percent last month, as COVID-19 restrictions curbed the activities of would-be shoppers, it follows a 0.7 percent drop in November.

The EU's biggest economies performed slightly better than expected in the last three months of the year, according to data just out. France's GDP (gross domestic product) figures fell by minus 1.3 percent, still ahead of the 3.9 percent expected. Spain's economy, which had widely been expected to contract, surprised analysts with 0.4 percent growth, while Germany squeaked home with a 0.1 percent rise. 

Republic of Korea conglomerate SK Innovation says it is to build Europe's largest battery plant in Hungary. The factory at Ivancsa, 50km south of Budapest, will be its third battery plant in Hungary, employing 2,500 workers and will benefit from an unspecified government subsidy. 

Shares in Dr Martens, maker of the iconic British boot, jumped 18 percent on its London market debut, valuing the firm at more than $5 billion. Private equity group Permira Holdings, which bought the company in 2014 for $460 million, said it was "delighted by the strong levels of interest … from institutional investors."

Watch: A toy doll is being used to help gauge air quality levels in Antwerp, Belgium.

Thousands of amateur investors have been pouring into the stock of video retailer GameStop, forcing Wall Street to take billions of dollars in losses and creating a ripple effect through other companies. Shares in GameStop have now risen more than 700 percent since last week. CGTN Europe was joined by Santosh Rao, head of research at Manhattan Venture Partners, to discuss the extraordinary recent shareholder action.   

I think this is sensational ….But when you step back a little bit, shorting has been an essential part of investments for a long time, you need it, it's a good strategy, it keeps the market honest. 

In this case, there was a technical factor where 140 percent of the shares of GameStock were shorted … So I think smart investors took advantage of that. Normally in the past, it was the sophisticated hedge fund and institutional investors who did that, but in this case, it was the small guy, the retail cohort, which is a rising force in the investment population. 

But I think in this case there was a socioeconomic twist to it. It was a sense that the retail investor has been shut out of this whole thing, the whole party, the fear of missing out, they all want to be part of it. And they can be now with fractional trading technology … so they can participate equally forcefully as their institutional guys. And that's what's happening. 

What do you see happening next? 

The regulations need to be tightened a little bit. They're not going to stop short trading but I think it's going to become more rational. When an investor comes in to short the stock, he's going to look at what's going on. Is it reasonable? Is it really detached from the fundamentals? And he's going to take a short position, is going to hedge his position or whatever. So I think what's going to happen now is people are going to be more careful. 

It's not going to be easy, just because the stocks are mispriced in terms of valuation, that you just go out and do it. I think you're going to study it much more carefully. The retail investors are also going to participate. So now I think everyone's going to be more cognizant of the competition of the players in the room and the regulations on the edges, the margin requirements and all of that will be tightened. 

So I think in the end it's going to be net positive for the market. In the meantime, there are going to be plenty of millionaires. And then a lot of people who are going to lose money.

And finally, the level of liabilities held by public corporations across EU member states in 2019 has just been revealed. Even before the outbreak of COVID-19, liability levels were running at 124 percent of GDP in Greece, and 96 percent in the Netherlands, but falling away in Eastern European nations. Analysts point to costly state guarantees on deposits held in public banks, a burden that looks set to increase as the recovery gets under way.