NEW YORK, Aug 10 (Reuters) - McKesson Corp MCK.N said on Monday it has widened its vaccine-distribution contract with the U.S. government to include preparations for distributing H1N1 flu vaccines now under development, sending its share higher.

McKesson already distributes about 80 million doses of various other vaccines, involving more than 40,000 providers, to U.S. adults and children through an existing contract with the Centers for Disease Control and Prevention.

“The H1N1 vaccine distribution effort will include the centralized distribution of the H1N1 flu vaccine to as many as 90,000 sites across the country, making it the largest public health initiative in the CDC’s history,” McKesson said in a release.

McKesson, whose shares were up 1.6 percent on the New York Stock Exchange in midday trading, said it would distribute H1N1 vaccines to sites designated by state health departments across the country.

Health experts have said that infants and children have been especially susceptible to infection with the H1N1 strain of the flu virus.

The H1N1 flu outbreak, declared a pandemic in June, has spread around the world and could eventually affect 2 billion people, according to World Health Organization estimates.

The virus has killed more than 800 people worldwide since emerging in April. (Reporting by Ransdell Pierson; Editing by Steve Orlofsky)