As of Dec. 26, the U.S. Centers for Disease Control and Prevention (CDC) has confirmed 12 cases - since August - of human infection with a swine-origin influenza A (H3N2) virus. This virus carries the M gene from the 2009 H1N1 virus that sickened more than one million people and killed another 477 in the U.S.

Cases of H3N2 have been reported in Iowa, Indiana, Maine Pennsylvania and West Virginia. The latest three cases occurred in two children who attended the same day care in West Virginia and a man from Indiana who worked with swine. All 12 patients have recovered fully.

Most cases only report a mild illness, with three of the 12 requiring hospitalization for recovery. Since human-to-human transmission has not been sustained, the CDC gives no indications that this strain could lead to a repeat of the 2009-2010 H1N1 pandemic.

"Nonhuman influenza virus infections rarely result in human-to-human transmission, but the implications of sustained ongoing transmission between humans is potentially severe," the CDC wrote. And although the H3N2 strain is different enough from the seasonal flu virus and the flu vaccine is "not expected to provide significant protection," the CDC does urge everyone to get vaccinated.

Read the full report here, but for additional information on the H3N2 virus, visit the CDC website.