UPDATE 2-Chugai to boost supply of Tamiflu for Japan

* To obtain supplies of Tamiflu for 12 million more people

* Additional supply is triple the amount shipped last season

* Chugai shares rise 0.5 pct, versus Nikkei's 1.3 pct gain

TOKYO, Sept 7 (Reuters) - Japan's Chugai Pharmaceutical Co Ltd (4519.T), a subsidiary of Swiss drugmaker Roche Holding AG (ROG.VX), said it plans to boost supply of the influenza drug Tamiflu in Japan to treat an additional 12 million people through March 2010.

The new H1N1 influenza virus, from which about 3,000 people have died worldwide, has killed 10 people in Japan.

The Japanese government has decided to increase stockpiles of antiviral drugs to 45 percent of the population to deal with the virus.

Chugai's additional supply is equivalent to three times the amount it shipped to medical institutions in the last flu season, Chugai said in a statement. The drugmaker's current stockpile is for 2 million people in Japan.

Chugai said it would consider obtaining more supplies if needed.

Among other Japanese drugmakers, Shionogi & Co (4507.T) aims to launch a new influenza drug by next autumn and Daiichi Sankyo Co (4568.T) plans to file for approval of a new drug by March 2010. Unlisted Toyama Chemical is also developing an influenza drug.

Shares of Chugai closed up 0.5 percent at 1855 yen, underperforming the benchmark Nikkei average's .N225 1.3 percent rise. (Reporting by Nobuhiro Kubo; Editing by Chris Gallagher)