GlaxoSmithKline sued Pfizer on Wednesday over patent infringement, alleging the US drugmaker's RSV vaccine steals key elements of the British company's version.

The case, filed in federal court in the state of Delaware, pits the producers of the only two approved vaccines for respiratory syncytial virus (RSV) against each other.

The United States on May 3 approved GSK's Arexvy as the first vaccine for RSV; that was followed on May 31 with US approval of Pfizer's Abrysvo. Both vaccines have since been approved by the European Union. 

"Upon information and belief, Pfizer knowingly uses GSK's claimed inventions in Abrysvo without permission," said the GSK complaint.

The complaint describes Arexvy as "the result of more than 15 years of research and development by GSK scientists," adding that Pfizer's program on an RSV vaccine began "no earlier than 2013."

The lawsuit lists four GSK patents granted by US officials between 2013 and 2023 that Pfizer is alleged to have infringed.

The suit seeks compensation for lost profits and royalties and a permanent ban on Pfizer selling the product in the United States.

RSV is a widespread, highly contagious pathogen most known for causing bronchiolitis -- an irritation and inflammation of the small airways -- in young children, especially in winter.

It also infects adults and can become dangerous in the elderly, who may develop pneumonia.

Pfizer did not immediately respond to a request for comment.

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