TORONTO - Health Canada has shortened the shelf life of unused supplies of GlaxoSmithKline's adjuvanted H1N1 vaccine after testing showed some lots are losing their punch.
The potency loss doesn't affect the safety of the product, Health Canada said in a release Friday. It relates only to how long surplus doses of the GSK vaccine can be stored for future use.
The move cuts the expiration date to six months from the 18 months originally listed. Federal officials could not say Friday whether the shortening of the shelf life means any portion of Canada's large vaccine surplus has now expired and must be destroyed.
"There are approximately 17.6 million H1N1 adjuvant doses currently held in federal and provincial stockpiles," Jirina Vlk, a spokesperson for the Public Health Agency of Canada, said in an email.
"PHAC is working with PTs (provinces and territories) and HC (Health Canada) to assess the impact that a new expiry date will have on our remaining H1N1 adjuvant vaccine doses."
It's conceivable that British Columbia could have some expired vaccine on its hands, admitted Dr. Perry Kendall, the province's chief medical officer of health.
"B.C. potentially does as some of our earlier lots would, with the new expiry date, have expired Mar 31st," he said by email. But Kendall noted the first affected lots were released early in the H1N1 vaccination effort, when public demand for vaccine was high.
Vlk said Canada had informed the World Health Organization about the expiry date change and was looking into whether the move has an impact on the five million doses of vaccine Canada donated to the Geneva-based global health agency.
The WHO is redistributing vaccine from donor countries and pharmaceutical companies to developing countries which didn't have pandemic contracts.
Canada bought just over 50 million doses of H1N1 vaccine and the bulk of it included adjuvant, a compound that boosts the immune system's response to the vaccine.
The expiration date change does not affect supplies of GSK's non-adjuvanted vaccine. The expiry date for that product remains at 18 months.
This is at least the third potency-related problem identified with H1N1 vaccine internationally, though it is unclear at this point whether that is a pattern or coincidence.
In late December, the U.S. Food and Drug Administration recalled lots of MedImmune's nasal spray vaccine because of potency loss. In early February, a similar problem prompted the FDA to recall lots of pediatric H1N1 vaccine made by Sanofi Pasteur.
Neither of those recalls involved adjuvanted vaccine. And neither of those companies sold pandemic vaccine to Canada.
The loss of potency in the GSK product was noticed in routine testing that Health Canada and the manufacturer conduct as part of Canada's pandemic vaccine contract.
Gradual potency loss would be expected over time, though seasonal flu shots generally have a shelf life of 12 months. It's not clear why the adjuvanted vaccine would lose potency so quickly or why the problem affected only the adjuvanted product.
"Health Canada, GSK, international regulators, the WHO and the vaccine manufacturers are discussing the possible causes, but it is still speculative at this time," Christelle Legault, a spokesperson for Health Canada, said Friday in an interview.
One possibility might relate to the differences in dose size, suggested Dr. John Treanor, a flu vaccine expert at the University of Rochester, N.Y.
GSK's adjuvanted flu shots have about a quarter of the antigen -- the active ingredient in vaccine --used in unadjuvanted shots.
"It's possible that the same rate of decrease in content would affect something that starts out with a lower dose more," Treanor said.
