The current recommendation is based on unique conditions associated with the existing pandemic, including low levels of population immunity to 2009 H1N1, the potential for health-care personnel to be exposed to H1N1 patients, and other factors, Dimond says.

CNN: STORY HIGHLIGHTS

His immunity would be low.

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Immunity to dengue is low in Singapore's population because of the intensive dengue-carrier controls, "making the population vulnerable to outbreaks, " said Ng Lee Ching, director of the Environmental Health Institute at Singapore's National Environment Agency.

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It is thought that the contentious issue of providing U.S. troops immunity from Afghan law is a low priority for the Afghan government in the negotiations.

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