Glaxo H5N1 vaccine may work against multiple strains

Editor's note: This story was revised Mar 7 to clarify information about global influenza vaccine production capacity.

March 6, 2007 (CIDRAP News) – The British pharmaceutical company GlaxoSmithKline (GSK) unveiled new findings yesterday suggesting that its inactivated H5N1 influenza vaccine may protect humans from more than one strain of the virus, which may build a stronger case for prepandemic vaccination and spur more countries to consider stockpiling.

Researchers from GSK detailed recent findings from two studies at a symposium in Hong Kong, the company said in a press release yesterday. In July 2006, the company had reported that its vaccine triggered a good immune response in humans at a much lower dose than other H5N1 vaccines under development.

GSK's vaccine, based on an H5N1 virus collected in Vietnam in 2004, contains a proprietary adjuvant (an immune-stimulating chemical). Adjuvants enable vaccine makers to produce more doses from a limited supply of antigen.

Though the GSK vaccine is made with older egg-based production methods, which are slower and more laborious than newer cell-culture or DNA technology, the dose-sparing effect of the adjuvant is crucial. The current world population is more than 6 billion, but the World Health Organization (WHO) has estimated the maximum global production capacity for seasonal flu vaccines at only about 350 million doses.

In November, the WHO cautioned governments against spockpiling prepandemic vaccines, because many fundamental questions about H5N1 vaccines remained, such as whether vaccines would work against more than one strain of the virus.

However, vaccines that are effective against more than one strain could strengthen the case for building prepandemic vaccine stockpiles. David Stout, president of GSK Pharmaceuticals, commented in the press release, "We believe this vaccine will provide governments with a new option to help protect their populations against the threat of a future human influenza pandemic."

Study results
The first study GSK presented at the Hong Kong meeting involved 400 adults and found that very low levels of GSK's inactivated, adjuvanted H5N1 vaccine (two 3.8-microgram [mcg] doses administered 21 days apart) elicited strong cross-reactive immunity against an Indonesian strain of the virus. The response was 25 times greater than that observed in a control group that received a nonadjuvanted version of the vaccine, GSK said in its press release. Immunity was assessed by measuring the level of neutralizing antibodies.

"This means that proactive administration of our prepandemic vaccine before or just after the start of a pandemic could help to substantially slow down the spread of the disease," said Jean Stephenne, president of GSK Biologicals.

For comparison, an H5N1 vaccine made by Sanofi Pasteur that was recently recommended for approval by a US Food and Drug Administration panel required two 90-mcg doses to yield an immune response in less than half of patients tested.

In the second study, researchers immunized ferrets with the GSK vaccine and then infected them with an Indonesian strain of H5N1 virus. Only 1 of the 23 infected animals died, which translates to a 96% protection rate, GSK reported.

Findings difficult to evaluate
Gregory Poland, MD, a vaccine expert at the Mayo Clinic in Rochester, Minn., told CIDRAP News that it's hard to evaluate GSK's findings, because the company has not yet published any clinical trials in peer-reviewed medical journals. "It's certainly exciting news, but it needs to be confirmed," he said. Researchers are eager to learn more about the adjuvant that GSK used, particularly its safety profile and reactivity.

The report of a robust immune response with a low dose of vaccine is promising, and in a prepandemic setting, a two-dose course isn't likely to be problematic, said Poland, who is a professor of medicine in infectious diseases at the Mayo College of Medicine and directs the Mayo Vaccine Research Group and Program in Translational Immunovirology. "It's tempting to go overboard, and I'm excited, but cautiously so," he added.

Besides positioning its vaccine as a prepandemic measure for national stockpiles, GSK would also like to market the vaccine someday to medical clinics and individuals, according to a Canadian Press story published yesterday.

In November 2006, the US Department of Health and Human Services awarded GSK a $40 million contract for a supply of its H5N1 antigen in bulk form, and in January it granted the company $63.3 million to develop antigen-sparing H5N1 influenza vaccines.

See also:

Jul 2006 CIDRAP News article "Glaxo says its H5N1 vaccine works at low dose

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