Government scientists are moving a step closer to a possible swine flu vaccine, analyzing two candidate viruses that might be used to brew one.

The Centers for Disease Control and Prevention hope to send one or both of those candidates to vaccine manufacturers by the end of next week, so they can begin the monthslong work of producing pilot lots of vaccine.

The candidate ingredients are a mix of genes from the new swine flu virus itself with components of other viruses that allow them to grow better in eggs, a key to flu vaccine production. The CDC says it is analyzing those two candidate viruses for signs that they could induce immune protection.