GlaxoSmithKline has received a complete response letter from the US Food and Drug Administration for its pandemic influenza A vaccine, called Q-Pan H5N1, despite getting unanimous backing from one of the agency's advisory panels last year.

The product is intended for the prevention of disease in adults who are at increased risk of exposure to the H5N1 influenza virus subtype contained in the vaccine. GSK says the CRL was "triggered due to an administrative matter that has recently been rectified" and it is working with the FDA to complete the review "in a timely manner".

In November 2012, the FDA’s Vaccines and Related Biological Products Advisory Committee voted unanimously 14-0 that the safety and immunogenicity data of the H5N1 adjuvanted influenza vaccine supported its approval for bird flu. However since then, concerns have arisen about a similar GSK vaccine called Pandemrix which uses the same adjuvant, ASO3, which boosts the response to the treatment.

The European Medicines Agency began a review to investigate a possible link between Pandemrix and narcolepsy, following an increased number of cases among children and adolescents in Finland and Sweden, following the H1N1 pandemic vaccination campaign in late 2009 and early 2010. A recent study published last month found that children in England who received Pandemrix vaccine during the 2009-2010 swine flu pandemic had a 14-fold heightened risk of developing narcolepsy.

Meantime, the FDA also issued a CRL to United Therapeutics Corp for an oral version of Remodulin (treprostinil), the second time the treatment of pulmonary arterial hypertension has been rejected by the agency.

Martine Rothblatt, United's chief executive, said that "we remain confident that oral treprostinil will play an important role in treating PAH and we are committed to working collaboratively with the FDA to accomplish this goal in the most timely and appropriate manner". However, some observers fear the worst.

Remodulin, which is injected, brought in $458 million in sales last year, about half of United's revenues.