Hours before US regulators are expected to approve one of its smallpox vaccines, the UK’s Acambis has won a court battle in its long-running dispute with Danish rival Bavarian Nordic over another jab for the same disease.

A court in Delaware ruled that Bavarian’s allegations that Acambis had improperly obtained and converted the modified vaccinia Ankara (MVA) strain that makes up its MVA3000 smallpox vaccine “was without basis in law or fact” and the charge that it had engaged in unfair competition and trade practices was also rejected. The case was dismissed in its entirety and the trial, which was due to be heard on June 5, has been cancelled.

Chief executive Ian Garland said that the decision “confirms our position that Acambis did not engage in improper conduct in developing our MVA3000 vaccine”. He noted that this is the second time the firm has litigated claims by Bavarian relating to MVA and the second time that the court has ruled in the UK biotechnology group’s favour.

However Bavarian is not taking the court’s verdict lying down and immediately launched an appeal. The firm had alleged that Prof Anton Mayr, the pioneering creator of MVA, which is used to make Bavarian’s own smallpox vaccine Imvamune, had supplied a sample to a scientist for research purposes only but Acambis received reproduced MVA virus material from it to produce MVA3000. If the Delaware court’s ruling is upheld, Bavarian argues that it “ would eliminate the value of man-made biological material”.

Peter Wulff, the Danish firm’s chief executive, said the firm is “confident that this decision will be reversed on appeal” as “the order basically holds that anyone can use a live biological material as the starting material, however obtained, and avoid liability for conversion by simply reproduce the material.” The companies are awaiting a date for a re-trial in the first patent infringement case, which was won by Acambis, but is being re-examined by the International Trade Commission.

Last November, Acambis and US partner went up against Bavarian to compete for a lucrative contract from the US government to stockpile smallpox vaccines, but Acambis was ruled out of the running because its tender was deemed to be “uncompetitive.” Bavarian’s bid was the only one left standing “has no significance on the final discussions with the US Department of Health and Human Services on the sole-award contract for an MVA-based smallpox vaccine.

Acambis was still celebrating the news that a US Food and Drug Administration review has just given a positive opinion for another vaccine, ACAM2000, and proposed it be indicated for the prevention of smallpox.

An FDA advisory committee meets later today to decide whether to recommend the vaccine for marketing approval and a final ruling will be made before the end of August. The agency’s green light is required before the US government finalises a contract with Acambis to provide on-going manufacturing of the vaccine for stockpiling.