Health officials alerted doctors Tuesday to a unique type of swine flu diagnosed in two California children, but it’s unclear whether many people will be susceptible to the infection.

“CDC is concerned, but that’s our job,” said CDC spokesman Tom Skinner.

CDC received reports of approximately one human swine influenza virus infection every one or two years. But more than a dozen cases of human infection with swine influenza have been reported since late 2005.

The new flu contains a unique combination of gene segments that have not been seen in swine or human flu viruses before,

In 1976, health officials were frightened by unusual cases of swine flu in soldiers at Fort Dix, N.J. The virus appeared to be similar to a deadly flu that killed millions around the world in 1918 and 1919.

Federal officials vaccinated 40 million Americans

Nevada

alert

seven cases of swine flu