U.S. drug regulators issued generally positive comments Monday about the effectiveness of a new experimental flu vaccine from MedImmune ( MEDI) called FluMist, but concerns over increased incidences of asthma and wheezing in children under 5 were highlighted.

A staff report from the Food and Drug Administration reviewing FluMist was posted on the agency's Web site Monday morning in advance of an independent advisory panel meeting Tuesday to discuss and vote on the approvability of the drug.

The report did not specifically recommend FluMist's approval, but said FluMist, given as a squirt up the nose, was effective in preventing the flu in healthy children. For children younger than 5, FDA reviewers were concerned about elevated rates of asthma and wheezing.

MedImmune has previously stated that it won't seek initial FluMist approval for children under 5 because of these safety issues.

The FDA's Vaccines and Related Products Advisory Committee will meet Tuesday to issue a recommendation on FluMist, which is being co-developed by Wyeth ( WYE).

In recent trading, shares of MedImmune were up 41 cents, or 1.5%, to $27.05. Wyeth shares were up 13 cents, or 0.3%, to $38.52.