Asian shares were mixed Tuesday, as optimism set off by a rally on Wall Street was dampened by concerns over the potential impact of the omicron variant of coronavirus.

Japan’s benchmark Nikkei 225 jumped nearly 1.0% to 28,960.31 in morning trading. South Korea’s Kospi gained 0.1% to 3,002.72. Hong Kong’s Hang Seng fell 0.1% to 23,201.42, while the Shanghai Composite dipped 0.2% to 3,610.32. Trading was closed in Australia for Boxing Day.

Also Read: Stocks that should be on your watchlist on Tuesday, December 28, 2021

Much of Asia has yet to see surges in infections of the omicron variant already playing out in other parts of the world, but experts are warning the region likely won’t be spared.

Japan has yet to see such a wave of new cases. Many areas are bustling with yearend shoppers, and many events are being held with spectators, although most people are wearing masks.

New daily cases in Japan have totaled about 200 lately. There have been relatively few COVID-related deaths so far with some recent days having none. Still, analysts warned uncertainties lie ahead.

“Record rallies are a tad too optimistic,” said Vishnu Varathan of Mizuho Bank, pointing to huge numbers of omicron cases in Europe and the U.S.

Technology companies led U.S. stocks broadly higher on Monday, extending the market’s recent rally and nudging the S&P 500 to another all-time high.

Wall Street kicked off the final week in a banner year for the stock market with mostly muted trading as investors returned from the Christmas holiday and several overseas markets remained closed.

The S&P 500 rose 1.4% to 4,791.19, its fourth straight gain. The benchmark index, which capped a holiday-shortened week Thursday with a record high, is on pace to close out the year with a 27.6% gain. It has notched 69 all-time highs so far this year.

The Dow Jones Industrial Average rose 1% to 36,302.38 and the technology-heavy Nasdaq rose 1.4% to 15,871.26.

The major indexes posted weekly gains last week as fears ebbed about the potential impact of the COVID-19 omicron variant. However, much is still uncertain about omicron, which is spreading quickly and prompting a return to pandemic restrictions in some places.

Small company stocks also rose. The Russell 2000 index gained 0.9%, to 2,261.46.

Trading is expected to be quiet but potentially volatile this week as the omicron coronavirus variant continues to spread quickly throughout the U.S. and overseas. However most big investors have closed out their positions for 2021, and are like to hold their ground until next week.

Airline stocks closed lower on the news of pandemic-related cancellations. Delta Air Lines fell 0.8% and United Airlines slipped 0.6%.

Also Read: Stocks open modestly higher as traders return from holiday

Shares in cruise line operators also fell. Norwegian Cruise Line slid 2.6% for one of the biggest declines in the S&P 500. Carnival dropped 1.2% and Royal Caribbean fell 1.3%.

Authorities in many countries have doubled down on vaccination efforts as omicron outbreaks complicate efforts stave off fresh lockdowns while hospitals are still under strain from delta variant infections.

In energy trading, benchmark U.S. crude added 27 cents to $75.84 from $75.57 a barrel in electronic trading on the New York Mercantile Exchange. It gained $1.78 on Monday to $75.57.

Brent crude, the international standard, rose 27 cents to $78.87 a barrel.

In currency trading, the U.S. dollar slipped to $114.86 from $114.87. The euro cost $1.1325, inching down from $1.1327.