According to final results, the Dow Jones index rose 0.10% to 35,754.75 points.

The technology-intensive Nasdaq climbed 0.64% to 15,786.99 points.

The S&P 500 gained 0.31% to 4,791.21 points

Optimistic at the start of the session, the indices were more volatile in the second half of the day, as investors remained concerned about the impact of the variant on travel.

British Prime Minister Boris Johnson's announcement of tightening restrictions to curb the spread of the Omicron variant of the coronavirus in the UK also dampened enthusiasm, analysts from Wells Fargo said.

Downing Street called for a return to telework on Monday and wants to implement the vaccination passport for certain large gatherings.

The clues were first supported by the announcement Wednesday by Pfizer and BioNTech that a third dose of their vaccine would neutralize the variant of the coronavirus Omicron.

According to studies carried out by the two laboratories, "the vaccine is still effective against Covid-19, also against the Omicron variant, if it has been administered three times", but this variant is "probably not sufficiently neutralized after two doses ".

Pfizer said it is working "on the development of a vaccine specific to the Omicron variant" and hopes to make it available by March.

Pfizer stock, in the green at the opening, lost 0.62%.

Merck, which has developed an anti-Covid pill to treat certain adults at risk, already marketed in Great Britain, has climbed 1.25%.

Investors were also encouraged on Wednesday by the progress of negotiations in Congress on the debt ceiling.

The House of Representatives voted on a roadmap to push through an increase in the debt ceiling which already "reduces the risk of a US default this month," said Art Hogan of National Securities .

At the macroeconomic level, the Bank of Canada's monetary meeting was on traders' radar as inflation hit a twenty-year high in Canada and the central bank has already ceased its monetary support program to the economy for face the health crisis.

The markets will also watch for inflation in the United States (CPI) published Friday for November.

Analysts estimate that the consumer price index will peak at 6.7% over one year against + 6.2% the month before.

Over one month, they forecast + 0.7% against + 0.9% in October.

These figures will support the US central bank, the Fed, in its intention to accelerate the reduction in its asset purchases, which will open the door to a rate hike in mid-2022.

"It is almost certain that the Fed will make this announcement," said Patrick O'Hare, while the monetary meeting is being held on December 14 and 15.

Yields on 10-year Treasuries rose to 1.52% from 1.45%.

In Congress, the boss of Instagram, a subsidiary of Facebook testified before a commission while elected officials assess the impact of the social network on adolescents.

Adam Mosseri assured parliamentarians that Instagram could "help" young people in difficulty, taking the opposite view of recent accusations against the social network.

The Facebook (Meta) title closed up 1.83% to $ 291.75.

Apple, one of the most massive capitalizations on Wall Street, still gained 2.28% to 175 dollars on Wednesday after having already pulled the rise of the Nasdaq since Monday.

The iphone maker has been hailed after being granted a delay in the lawsuit against game publisher Epic Games to modify its app store.

The American company Planet, which takes images of the Earth from satellites and analyzes them, made a hesitant entry on Wall Street via a merger with a company already listed on the stock exchange which brought it in 590 million dollars.

After fluctuating sharply during the session, its title ended up 5% to 11.35 dollars.

That valued the company at around $ 490 million according to CNBC.

© 2021 AFP