The US Food and Drug Administration has approved four vaccines for the H1N1 influenza virus, while other companies, including GlaxoSmithKline (GSK, London), have reported promising results from clinical studies with a single-dose vaccine.

The approved vaccines are made by CSL (Melbourne, Australia), MedImmune (Gaithersburg, MD), Novartis Vaccine and Diagnostics (Basel) and Sanofi Pasteur (Lyon, France). According a Sept. 15 FDA release, all of the vaccines are manufactured using the same processes, which "have a long record of producing safe seasonal influenza vaccines".

Critically, data have shown that a single dose is enough to ensure immunity. "Based on preliminary data from adults participating in multiple clinical studies, the 2009 H1N1 vaccines induce a robust immune response in most healthy adults 8 to 10 days after a single dose," according to the release.

Meanwhile, data from a trial currently being conducted in Germany by GSK have also suggested that a single dose may be enough to ensure immunity. According to a statement issued by GSK, "The results demonstrate that after one dose the candidate vaccine can provide a strong immune response, which exceeds the immunogenicity criteria as defined by international licensing authorities for a pandemic influenza vaccine."

In the statement, Jean Stephenne, President GSK Biologicals, added, "This trial provides encouraging data on the potential use of a single dose of our pandemic vaccine. We have shared these data with both regulatory authorities and governments who are making key decisions on urgent global public healthcare at this time."

The company's next step is to complete the trial in Germany as well as 15 other studies, which are part of the vaccine's clinical development program. More than 9000 subjects, including healthy adults, the elderly and children, are taking part in the studies. GSK has said that the data will be submitted to regulators as soon as they are available.

Earlier this month in a press statement, Novartis reported that a single dose of its own vaccine "induced responses associated with protection against influenza." The vaccine has now been approved by FDA; however, in the statement, Novartis explained that the strongest responses were seen among subjects who received two doses.

It is not only Big Pharma that has reported progress on the H1N1 front. Variation Biotechnologies (Cambridge, MA) also claims that its own proprietary vaccine triggered a strong immune response and gave protection against the H1N1 strain in ferrets, which, according to the company, are the most predictive animal model of influenza in humans, reports Business Wire. However, the company does not anticipate initiating human trials until 2010.

The big question is will the vaccines be ready for the second wave of influenza cases, which is expected to occur in the northern hemisphere this winter? Although the majority of H1N1 patients experience mild illness, the World Health Organization has said in a briefing note on its website that, "Even if the current pattern of usually mild illness continues, the impact of the pandemic during the second wave could worsen as larger numbers of people become infected."

In the US, vaccines are close to being available following FDA approvals. According the FDA release, the "vaccines will be distributed nationally after the initial lots become available, which is expected within the next four weeks".