Adds details throughout

Feb 10 (Reuters) - Moderna MRNA.O said on Tuesday the U.S. Food and Drug Administration will not review its approval application for its influenza vaccine, sending shares of the company down 8% in aftermarket trading.

The FDA in its letter said the company's choice to compare mRNA-1010 to an already licensed standard-dose seasonal influenza was the sole reason for the refusal to initiate the review of Moderna's application.

Specifically, the letter cited the lack of an "adequate and well-controlled" study with a comparator arm that "does not reflect the best-available standard of care," Moderna said.

The letter did not identify any specific safety or efficacy concerns.

Moderna said last year the mRNA-1010 vaccine was 26.6% more effective than an approved annual flu shot from GSK GSK.L.

The vaccine maker said it has requested a meeting with the regulator to understand the path forward.

The development lands little over a month after the U.S. overhauled its longstanding guidance on childhood immunization and rolled back recommendation for routine vaccination against six infectious diseases, including influenza.