The "Formic Wars" comics contain new material that is not in the books. They are prequel stories. Here is the publisher description for "Formic Wars: Burning Earth" (7 issues originally):
The never-before-told prequel to ENDER'S GAME! An unidentified ship is rocketing toward Earth with tech far beyond anything we've ever seen, and the only people who can give warning are a small band of asteroid miners millions of miles from home. The clock is ticking, and it doesn't look good for the human race. From New York Times-bestselling author Orson Scott Card comes the tale of humanity's first contact with the Formics - and the horrible toll it took on mankind.
This is followed up by the 5 issue "Formic Wars: Silent Strike":
With 44 million people killed by the toxic gas the alien Formics unleashed in China, the only hope of a counter-agent lies with Mazer Rackham and the Mobile Operations Police safely retrieving a sample. Meanwhile, young asteroid miner Victor Delgado has snuck aboard the Formic mothership in hopes of taking it down alone - and boy is he is for a big disappointment. Meanwhile, Captain O'Toole and his unit take on the Formic Death Squads, but the humans are outnumbered a hundred to one! Besieged on all sides, the Formics fight to the bitter end - but as the Hegemon of Earth is revealed, is it truly the end after all?