BEIJING (AP) — Asian stock markets declined Friday as questions about the effectiveness of one possible coronavirus vaccine weighed on investor optimism.

Benchmarks in Tokyo, Hong Kong, Seoul and Sydney retreated while Shanghai gained.

Investors have been encouraged by reports of progress toward a possible vaccine. But they were uneasy after researchers questioned data that showed a candidate from the University of Oxford and AstraZeneca was 70% effective.

“Market participants showed increasing signs of nervousness as data errors were revealed,” said Mizuho Bank in a report.

The Nikkei 225 in Tokyo lost 0.1% to 26,506.97 and Hong Kong’s Hang Seng sank 0.2% to 26,761.22. The Shanghai Composite Index added 0.4% to 3,383.06.

The Kospi in Seoul lost less than 0.1% to 2,625.84 and Sydney’s S&P-ASX 200 fell 0.7% to 6,592.50. New Zealand and Jakarta gained while Singapore retreated.

U.S. markets were closed Thursday for a holiday.

Investors are looking forward to a possible vaccine to control the coronavirus following the deepest economic slump since the 1930s, though forecasters warn the stock market rebound might be too early to be sustained.

Those hopes were dented this week when researchers questioned how Oxford and AstraZeneca calculated the effectiveness of their vaccine. That alliance is among researchers who have reported the most progress toward a possible vaccine. The AstraZeneca CEO told Bloomberg News the company might conduct another trial.

Investors also are dismayed that U.S. states and European governments are reimposing controls on business and travel as infection rates surge.

The disease has killed more than 1.4 million people worldwide and there are 61 million confirmed cases, according to data gathered by Johns Hopkins University.

Markets are uneasy about U.S. data showing consumer spending weakening and job losses rising.

Supplemental unemployment benefits that supported consumer spending, the engine of the U.S. economy, have expired. Congress is deadlocked on a possible new aid plan.

In energy markets, benchmark U.S. crude lost 67 cents to $45.04 per barrel in electronic trading on the New York Mercantile Exchange. Brent crude, used to price international oils, lost 11 cents to $47.90 per barrel in London.

The dollar fell to 104.07 yen from Thursday’s 104.25 yen. The euro rose to $1.1920 from $1.1906.