WHO experts: Single dose of swine flu vaccine may be enough

The group also concluded that every vaccine that has been approved by a government regulatory authority around the world appeared safe, including for pregnant women. That includes vaccines with a substance known as an "adjuvant," which boosts the effectiveness of the vaccine, allowing available stocks to be divided into more doses.
Despite an emergency program to produce the vaccine in the United States and elsewhere, demand for the vaccine so far has outpaced supply in many countries. The United States has not yet approved any vaccine that includes an adjuvant.