LONDON Pfizer and Moderna's legal battle over their rival Covid-19 vaccines looks set to continue after London's High Court gave a mixed ruling on two of Moderna's patents, likely prompting a flurry of appeals in the London leg of the litigation.

Pfizer and its German partner BioNTech sued Moderna in London in September 2022, seeking to revoke two patents held by Moderna, which hit back days later alleging its patents had been infringed.

The competing lawsuits over the companies' two vaccines, which helped save millions of lives and made the companies billions of dollars, are just one strand of ongoing litigation around the world focusing on messenger RNA (mRNA) technology.

Moderna had argued Pfizer and BioNTech copied mRNA advances it had pioneered and patented well before the Covid-19 pandemic began in late 2019.

US-based Moderna was seeking damages for alleged infringement of its patents by Pfizer and BioNTech's Comirnaty shot on sales since March 2022.

Pfizer made US$11.2 billion in sales from Comirnaty last year, while Moderna earned US$6.7 billion from its vaccine Spikevax, illustrating the potentially huge sums at stake.

Pfizer and BioNTech, however, asked the High Court to revoke Moderna's patents, arguing that Moderna's developments of mRNA technology were obvious improvements on previous work.

The High Court ruled on Tuesday that one of Moderna's two patents relating to mRNA technology was invalid, but that another similar patent was valid and that Pfizer and BioNTech's Comirnaty vaccine had infringed it.

All three companies said they disagreed with the parts of the court's decision on which they lost, and it is expected that all parties will seek permission to appeal.

Pfizer and BioNTech said in a statement: "These proceedings have no bearing on the safety and efficacy profile of our vaccine, as established by regulators worldwide.

"Irrespective of the outcome of this legal matter, we will continue to manufacture and supply the Pfizer-BioNTech Covid-19 vaccine in line with our agreements and established supply schedules."

A spokesperson for Moderna said the company was pleased the court "recognized the innovation of Moderna scientists by confirming the validity and infringement" of one of its patents.

Pfizer, BioNTech and Moderna are also involved in parallel proceedings in Germany, the Netherlands, Belgium and the United States, much of which has been put on hold, as well as at the European Patent Office.

The London ruling comes at a time of financial strain for Moderna, whose shares have plummeted by more than 70% since the peak of the pandemic as demand and sales for Spikevax have fallen. Shares of Pfizer, meanwhile, are down about 29% since mid-2021.