Such terms usually involve royalties on the sales of products using the licensed technology.

The new stance opens up the possibility of Moderna filing patent-infringement suits against companies in wealthier countries that don’t reach agreements on using Moderna’s technology, though it didn’t say when it might begin seeking to enforce its patents.

“If people have used, or are using our technology to make a vaccine, I don’t understand why, once we’re in an endemic setting when there’s plenty of vaccine and there’s no issue to supply vaccines, why we should not get rewarded for the things we invented,” Moderna Chief Executive

Stéphane Bancel

said in an interview.

Moderna, of Cambridge, Mass., has several patents in the U.S. and other countries covering various aspects of its Covid-19 vaccine, named Spikevax.

Some of the company’s patents claim the invention of aspects of the underlying technology, known as messenger RNA, while others cover the use of an mRNA vaccine against coronaviruses.

In 2020, Moderna pledged it wouldn’t enforce patents covering its Covid-19 vaccine for the duration of the pandemic. Under that pledge, Moderna didn’t bring any patent-infringement litigation against other companies or seek court injunctions to block the availability of vaccines.

Under its modified pledge, Moderna said it will never enforce its Covid-19 vaccine patents in 92 countries that are part of an international program, called Covax, that provides Covid-19 vaccines.

Those countries include India, Indonesia, Afghanistan, Haiti, Rwanda, Algeria, Egypt and Vietnam. Moderna said that its new pledge applies to Covid-19 vaccines that are manufactured solely for use in those 92 countries.

Moderna also said it wouldn’t enforce Covid-19 vaccine patents in South Africa against the efforts by Afrigen Biologics and Vaccines, working with the World Health Organization, to copy Moderna’s vaccine.

In lower-income countries, “we don’t want people to waste any time worrying about investing in Covid-19 vaccines using our technology,” Mr. Bancel said.

But the situation is different in higher-income countries, Mr. Bancel said, because vaccine supply in those countries is no longer limited.

Mr. Bancel declined to say if and when Moderna might begin enforcing its patents in higher-income countries.

The Covid-19 vaccine from

Pfizer Inc.

and

BioNTech SE

also uses mRNA technology. Pfizer has said it doesn’t expect intellectual property to be a barrier to its Covid-19 vaccine. The company has said it expects any third-party patent licenses to be available to it on reasonable terms.

Patent disputes surrounding Covid-19 vaccines have already broken out, however, with drug companies pitted against each other and government and academic scientists over who invented what.

Some poorer countries including India and South Africa have asked the World Trade Organization to waive certain patent obligations so that countries could more easily manufacture Covid-19 vaccines without running afoul of patent rights held by drug companies. Last year the Biden administration said it supported the move, while vaccine makers opposed it. It hasn’t been implemented, and is considered unlikely to happen.

Moderna is facing patent-infringement lawsuits. Last week, two small biotechnology companies,

Arbutus Biopharma Corp.

and Genevant Sciences Inc., filed a lawsuit in federal court in Delaware, alleging Moderna’s Covid-19 shot infringes on six of their patents.

The companies said they are seeking compensation for what they allege to be Moderna’s use of lipid nanoparticles—the tiny shells encasing mRNA in the vaccines—covered by their patents.

Moderna previously tried to invalidate some of the patents in U.S. patent-office proceedings, but lost a federal court appeal in December. Moderna denied the allegations and said it plans to defend itself in the lawsuit. Moderna said its vaccine uses its own proprietary lipid-nanoparticle technology.

Moderna also had a dispute with the National Institutes of Health over who can be listed as co-inventors in an application for a U.S. patent covering the mRNA sequence in the Covid-19 vaccine.

NIH researchers collaborated with Moderna on the vaccine’s design and testing, and objected to Moderna’s initial plan not to list the government scientists as inventors. Moderna has since dropped the patent application.

Moderna said the new patent pledge is part of its efforts to promote global health. The company also said Monday it plans to begin or advance testing of vaccines against 15 pathogens identified as being among the biggest public-health risks, such as Zika and tuberculosis.

On Monday, Moderna said it plans to build an mRNA vaccine manufacturing plant in Kenya, with a goal of eventually producing as many as 500 million vaccine doses annually for use in Africa.

Write to Peter Loftus at peter.loftus@wsj.com