UPDATE 1-Sanofi CEO: US H1N1 vaccine output rising quickly

* 75 mln H1N1 vaccine doses to ship in US by Christmas

* Sanofi expects first EU H1N1 approval "shortly" (Adds details on vaccine production, pending EU approvals)

By Ros Krasny

CAMBRIDGE, Mass., Nov 10 (Reuters) - Production of H1N1 swine flu vaccine at two U.S. facilities is "working optimally" with output on the rise, the chief executive of Sanofi-Aventis (SASY.PA) said on Tuesday.

The French pharmaceutical giant had shipped 14 million doses by the end of October and expects to have shipped some 75 million doses to the U.S. market by late December, CEO Christopher Viehbacher told reporters at a company-sponsored biotech event in Cambridge, Massachusetts.

"We're probably the only company that is producing reliably right now," he said. "We're pretty happy with production; it takes a while to get the thing up and running."

Production of the vaccine runs on roughly a 15-week cycle. While output has been coming up to speed and availability of the vaccine has been scarce in many areas, instances of swine flu in the United States have been spreading.

Sanofi-Aventis' facilities in Swiftwater, Pennsylvania, are the only sites producing the H1N1 vaccine in the United States,and are now using some 300,000 eggs a day, Viehbacher said.

Yields for H1N1 vaccine production are approaching levels typical of seasonal flu vaccine, which can also vary from strain to strain, he said.