By Blake Brittain

(Reuters) -British biopharmaceutical giant GSK sued Pfizer in a U.S. court on Wednesday, alleging that Pfizer's respiratory syncytial virus (RSV) vaccine Abrysvo violates GSK's patent rights in its rival RSV shot Arexvy.

In the lawsuit brought in federal court in Delaware, GSK said New York-based Pfizer's vaccine infringes four of its patents related to the antigen its shots use to fight the respiratory disease.

Pfizer said in a statement that it is "confident in its intellectual property position" and will "strongly defend" its right to bring Abrysvo to patients.

Both vaccines were approved by the U.S. Food and Drug Administration in May for use in adults over age 60. They are the first vaccines approved to prevent RSV, which causes around 14,000 deaths in adults 65 and older in the United States annually, according to government estimates.

Pfizer and GSK are running a tight race to tap into the RSV vaccine market, which could exceed $10 billion by 2030, according to analysts. The vaccines are part of both companies' strategies to replace aging drugs that will face cheaper generic competition.

A GSK spokesperson said in a statement that intellectual property protections are the "foundation of research-based companies' ability to drive innovation," and that the lawsuit should not affect GSK's ability to launch Arexvy.

GSK said in the lawsuit that Pfizer began working on its RSV program as early as 2013, at least seven years after GSK. The lawsuit said Pfizer knew of GSK's patented technology since at least 2019, when it began challenging the validity of European versions of the patents.

(Reporting by Blake Brittain in Washington; Additional Reporting by Michael Erman in New York; Editing by David Bario, Will Dunham, Mark Porter and Jonathan Oatis)