BioWorld International Correspondent

Allergy Therapeutics plc will have to conduct a new U.S. trial of its hay fever allergy vaccine at an additional cost of £10 million (US$20.3 million) after one subject suffered an adverse reaction, causing the FDA to put the trial on hold. This also will delay the launch of the product by 12 months.

The treating physician has changed her earlier opinion from saying that the reaction was "possibly related" to the Pollinex Quattro vaccine to saying it had other, unrelated causes. But the two week delay caused by the hold means not enough subjects can be vaccinated before the ragweed pollen season starts.

With the pollen season imminent, the trial had to be moved to the observation phase.

Prior to the clinical hold, 992 patients had been recruited, 92 percent of the target of 1,074.

Of those, approximately 300 have received all four injections and are considered to be participating in the study per protocol. Of the balance, about 300 had received three injections, 165 two and 227 one injection.

Worthing, UK-based Allergy Therapeutics said that while useful data will be collected from the study, it is compromised to the extent it is highly unlikely to reach its primary endpoint. The completion of the program will require a further study, probably to be conducted next year.

A final determination of how the study will be continued has not been made, but Gary Waanders, analyst at the house broker Nomura Code Securities, said he understood the study will recruit the remaining 774 subjects required to reach the initial target, with the data from the current 300 fully-dosed subjects potentially remaining blinded until the subsequent trial is completed.

Ibraheem Mahmood, analyst at Investec in London, said it seems unlikely that the diagnosis will be changed again, and he expects the FDA to remove the clinical hold. However, the one-year delay and the unforeseen cost of the new trial means that, as things stand, Allergy Therapeutics will run out of cash in the first half of 2009.

A parallel study of the vaccine in grass allergy was fully recruited, and all doses had been administered when the FDA clinical hold was applied.

While that will be completed as planned, the associated safety study cannot begin until the hold is lifted. As a result, the grass program will suffer some delay, the length of which depends upon when the clinical hold is lifted.

The company said it is investigating details of the adverse event and providing the FDA with new data as they are accumulated, adding it is confident that following the ongoing reviews, the FDA will accept the alternative diagnosis.