South Korean shares opened nearly flat Tuesday despite the overnight rally on Wall Street triggered by better-than-expected efficacy of a COVID-19 vaccine by Pfizer, as investors turned to profit-taking after a sixth straight rise.

The benchmark Korea Composite Stock Price Index (KOSPI) rose 0.5 point, or 0.02 percent, to 2,447.7 in the first 15 minutes of trading.

Stocks came to a muted start after hiking 1.27 percent on the Biden effect the previous session.

US top infectious disease expert Anthony Fauci said the Pfizer vaccine shot will have "major impact," fueling investor optimism that the vaccine could be deployed by the end of the year.

Overnight, the Dow Jones Industrial Average jumped 2.95 percent to close at 29,157.97 points. The Nasdaq Composite retreated 1.53 percent, but the S&P 500 advanced 1.17 percent.

In Seoul, most large caps traded lower.

Market bellwether Samsung Electronics shed 0.66 percent, while No. 2 chipmaker SK hynix gained 0.81 percent.

Leading chemical firm LG Chem lost 2.04 percent, and rechargeable battery maker Samsung SDI slid 0.56 percent.

Pharmaceutical giant Samsung Biologics added 0.92 percent, but Celltrion dipped 1.93 percent.

Hyundai Motor, the country's largest carmaker, moved up 0.29 percent.

Internet portal giant Naver fell 4.03 percent, and its rival Kakao dropped 3.63 percent.

The local currency was trading at 1,116.85 won against the US dollar, down 2.95 won from the previous session's close. (Yonhap)