Capt. Robert Magill (right), of Buffalo, N.Y., receives the H1N1 flu vaccine from Spc. Justin Roberts, Nov. 23. Photo by Sgt. Jon Soles, Multi-National Division - Baghdad.

"It is mandatory for all military personnel to get the shot," said Spc. Jennifer Laknahour, a medic from Milwaukee. "Everyone has to get it to go home. We will not sign your PDHA [Post-Deployment Health Assessment] unless you get the H1N1 shot."

Soldiers receive immunizations through the companies to which they are assigned, according to DSTB aid station non-commissioned officer in charge, Sgt. 1st Class Greg Wilson Jr., of Philadelphia.

Symptoms of H1N1 flu include fever, fatigue, sore throat, muscle aches, chills, coughing and sneezing. Diarrhea and vomiting may also occur. The H1N1 flu virus is a new, more serious strain of flu than typical seasonal flu viruses, according to the Center for Disease Control.