UPDATE 2-Roche/Novartis asthma drug effect modest-FDA staff

* Xolair benefit in 6-to-11-year-olds 'somewhat modest'

* FDA staff: No new safety issues in pediatric studies

* Safety questions remain about Xolair's use in children

* Both Roche, Novartis shares up 0.4 percent (Adds sales, background on medicine)

WASHINGTON, Nov 16 (Reuters) - An asthma drug from Roche (ROG.VX) and Novartis (NOVN.VX) has "somewhat modest" benefits for children aged 6 to 11, U.S. reviewers said in documents released on Monday.

Pediatric studies of Xolair have not revealed any new safety issues, but questions remain about use of the drug in this age group, Food and Drug Administration staff added in an analysis prepared for an advisory panel that meets on Wednesday.

The drug already is approved for adults and adolescents aged 12 and older. The companies are now seeking the FDA's permission to promote the injectable medicine for younger patients with moderate to severe asthma as an add-on to standard therapy.

In 2008, the drug generated sales of $517 million for Roche's Genentech unit and $211 million for Novartis. Novartis and Genentech jointly market Xolair in the United States, while Novartis markets it elsewhere.

Xolair was approved for use in children aged 6 to 11 years in Europe in August.

In July, the FDA said it was looking at whether Xolair was linked to an increased risk of heart attacks and strokes after preliminary results from a Genentech study raised concerns.

At the time, the agency said the results required further review, and it was not recommending any changes for use of Xolair.

Xolair works by disabling a naturally occurring antibody called IgE, which triggers the release of chemicals that cause inflammation and provoke asthma and allergy attacks. The drug's generic name is omalizumab.

Shares of both Novartis and Roche were up 0.4 percent on Monday. (Reporting by Lisa Richwine and Ben Hirschler, editing by Lisa Von Ahn)