As U.S. health officials struggle to vaccinate tens of millions of Americans against the pandemic of swine flu, some are looking regretfully at one easy way to instantly double or triple the number of doses available -- by using an immune booster called an adjuvant.
Influenza A (H1N1) virus is a subtype of influenzavirus A and the most common cause of influenza (flu) in humans. Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a large fraction of all seasonal influenza. H1N1 strains caused roughly half of all human flu infections in 2006. Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza).