The pharmaceutical manufacturer, based in the United Kingdom, produced the vaccine to protect the population in case of a pandemic, following an outbreak of H1N1 "bird flu" in 2009 that killed 17,000 by early 2010.
A spokesperson for the company said the delay was "due to an administrative matter that has been rectified," saying the postponement in regulatory approval was unrelated to recent controversy over its H1N1 vaccine, which has been linked to greater rates of narcolepsy in children. The drug maker "and the FDA are actively working together to complete the review in a timely manner," the spokesperson added.
European studies conducted last year showed an increase in narcolepsy cases due to the original H1N1 vaccine but concluded the benefits of vaccination outstripped the risk. In November, a 14-member advisory panel recommended unanimously the FDA approve the vaccine to protect against the newer H5N1 strain.
More recent studies conducted in Britain, however, suggest the risks might be greater than previously thought, with a more serious association between the H1N1 vaccine, Pandemrix, and narcolepsy cases. Manufactured in Québec, the vaccine is a two-component vaccine consisting of a monovalent, inactivated, split A/H5N1 influenza virus antigen and the AS03 adjuvant system. In clinical trials, people experienced adverse reactions of pain and swelling around the injection site, in addition to muscle aches, headache, joint pain, shivering and sweating.
An FDA spokesperson told media the regulator has no comment on the matter and no plans to reconvene a meeting of the advisory committee.
The World Health Organization in late summer of 2010 pronounced the bird flu pandemic over, with a return to more seasonal patterns. However, the organization issued a pandemic warning in April 2011 for the Americas, with particular focus on the Chihuahua region of Mexico.
The new virus, a subtype of influenza A virus, can cause illness in humans and many other animal species, with a version spreading globally by bird vector after first appearing in Asia. Alarming to public health officials, research shows only a few mutations would transform the virus from mild threat to a global pandemic, transmitted by airborne contact among humans and other mammals.