Canada's vaccine manufacturer says one dose – not two – of its new H1N1 drug offers enough protection from the pandemic influenza virus, which potentially means that the country may have ordered more vaccine than needed for its citizens.
Results from GlaxoSmithKline's first clinical trials in Germany showed that 98 per cent of healthy adults who received a shot containing 5.25 micrograms of antigen and the company's AS03 adjuvant – chemical boosters that can increase production – were protected from the virus when tested three weeks later.
Early studies from the United States and elsewhere also show that one H1N1 dose may be enough, which would make the logistics of a mass vaccination program a lot easier than originally believed.
When the virus first appeared, public health authorities worried that two doses, given about three weeks apart, would be needed to inoculate the public because H1N1 was a novel strain. With that in mind, Canada ordered 50 million doses from GSK for all Canadians who want and need the vaccine.
The Public Health Agency of Canada said yesterday the results from GSK are encouraging, but it was too soon to determine if just one dose was needed.
“Prudence dictates that we continue planning for a two-dose regime until we have more conclusive information on which to take a decision,” a spokeswoman said in an e-mail.
GSK is conducting another 15 studies in healthy adults, children and the elderly.
The German trials involved 130 healthy volunteers between the ages of 18 and 60. There were no figures on side effects, a company spokeswoman said. Other studies have shown that side effects from the H1N1 vaccine are similar to what is seen with the seasonal flu vaccine, which includes headaches and sore muscles.
Another issue has to do with the amount of vaccine in a dose. GSK plans to sell Canada a formulation containing 3.75 micrograms of antigen, less than what was used in the clinical trial, raising questions of whether the vaccine will work.
“Based on GSK's experience with its adjuvants systems, we do not anticipate that there will be any significant difference in the immune response elicited by the final formulation,” a company spokeswoman said.
Scott Halperin, director of the Canadian Centre for Vaccinology in Halifax, doesn't believe it will be an issue either. Still, he said, young children may require two doses, as with the seasonal flu vaccine. Clinical trials will offer more guidance, he added.
When asked if Canada ordered too much vaccine, Dr. Halperin responded: “Potentially.”
If further trials show that only one dose is needed, the federal government may be able to change its order. If it's too late to do so, it may choose to donate vaccine to the developing world.
“One had to place the order based on the best information available,” Dr. Halperin said. “And the best information with a pandemic strain is you might well need two doses, so I think that was definitely a right decision.”
