SHANGHAI/SUZHOU, China, April 19 (Reuters) - China's vaccine developers stuck with unused mRNA COVID shots and idle manufacturing plants are pursuing new targets for the novel messenger RNA technology, but they face a tough path, crimped by a lack of revenue.

Three Chinese companies - Walvax Biotechnology, CSPC Pharmaceutical Group and Stemirna Therapeutics - came up with mRNA vaccines that won limited emergency approvals in Asia.

However, Walvax and CSPC are not currently manufacturing three of their China market shots, a China health official told Reuters.

And Stemirna said in July it had halted work at a planned vaccine factory in Shanghai, citing lack of demand.

Their setbacks come just as Moderna, which developed one of the world's first mRNA vaccines against COVID, is setting up manufacturing in Shanghai, with plans to launch up to 15 new mRNA medicines in the next five years and bring up to 50 candidates into clinical trials.

"At the moment China's mRNA is still just taking off," a spokesperson for CSPC saidreferring questions on mRNA plans to a social media post highlighting a respiratory syncytial virus (RSV) vaccine candidate's application for clinical trials.

Walvax declined to comment.

MISSED OPPORTUNITY

Walvax working with biotechnology startup Abogen Biosciences came up with China's first domestically developed mRNA shot, and received approval from Indonesia in September 2022.

Stemirna and CSPC followed quickly, with Stemirna receiving approval from Laos, and CSPC and Walvax from China for similar shots.

However, Indonesia did not purchase Walvax's first shot, an Indonesia health ministry spokesperson told Reuters, without explaining why.

And in Laos, where Stemirna's shot has not been sold, vaccines need World Health Organization (WHO) approval and there are "enough (COVID) vaccines" for now, Kongxay Phounphenghack, head of vaccine preventable disease at the Laos health ministry's Mother and Child Health Center, told Reuters.

None of the Chinese developers sought WHO approval for their mRNA vaccines, that agency's China office told Reuters.

Construction of a Stemirna plant in Laos is "not yet" complete, said Davone Duangdany, director of the drug and medical device control division within the Laos health ministry.

Stemirna's CEO, Li Hangwen, declined to comment.

CSPC's first shot faced limited distribution by health authorities, partly because it did not target a more recent variant or had stricter storage and transport requirements than standard technology shots, staff at some medical institutions in China's two most populous cities, Beijing and Shanghai, told Reuters.

That shot was first administered in May 2023. CSPC has not announced the rollout of its updated shot and Walvax has said it is seeking further approval for its second shot, similarly designed for the Omicron XBB.1.5 variant.

OVERCOMING SETBACKS

Despite the weak demand, the drugmakers aren't giving up on launching mRNA vaccines just yet. Walvax, CSPC and Stemirna have said they are also researching other medicines including for infectious diseases and tumours.

"China is trying hard to develop in this direction," George Gao, a virologist at the Chinese Academy of Sciences Institute of Microbiology who previously led the Chinese Center For Disease Control and Prevention, told Reuters.

China's developers could support vaccine supply in Africa and Asia by producing at low cost and transferring knowledge, said Dicky Budiman, an epidemiologist at Griffith University in Australia who has advised Indonesia's government on COVID.

One study estimated the cost of building, equipping and replacing vaccine plants without subsidies in the U.S. or EU would be around $0.20 per dose annualised over the lifetime of a plant and equipment, but less in China.

However, the potential Moderna competitors face a long road ahead as they seek to bring their mRNA products through trials and to market.

CSPC has said it aims to launch shots for RSV in 2026 and for shingles in 2028. Walvax aims to launch a combined COVID and flu mRNA vaccine over the next five to 10 years.

But with limited markets for their existing vaccines, the three Chinese companies lag their rival Moderna in sales, potentially holding back their ambitions.

CSPC generated 31.45 billion yuan ($4.3 billion) in revenue in 2023 and Walvax $571.4 million, compared with Moderna's revenue of $6.8 billion in the same year.

In a further setback, CSPC's Malaysian research partner, Malaysia Pharmaniaga, is battling financial losses, and a spokesperson said mRNA vaccines are "not within Pharmaniaga's scope of business direction".

CATCHING UP

Robert Langer, an MIT engineer who was a co-founder of Moderna, told Reuters he expected Moderna and "possibly" BioNTech to dominate mRNA medicines for the next five to 10 years.

Langer cited Moderna's "huge technological and IP (intellectual property) advantages" and its headstart on the long timeframes needed to conduct clinical trials for new products.

A former Stemirna executive, Frank Zhang, said China's pharmaceutical industry cannot compete with innovative companies abroad because of gaps in technology, talent and ideas.

"A company able to gain market share in the U.S. is the only company with actual strength," Zhang, who led part of Stemirna's COVID vaccine R&D efforts, told Reuters.

Walvax has gained knowledge about large-scale production technology, and funding was not likely to be a problem for it or CSPC, given that both are listed companies selling other products, said Abogen's CEO Ying Bo, a former Moderna scientist.

But Ying said the long timeframes for researching, developing and winning approvals for mRNA vaccines pose a big challenge for Chinas developers.

"Time is always the biggest enemy to biotech," Ying said. (Reporting by Andrew Silver; Additional reporting from Stanley Widianto in Jakarta. Editing by Michele Gershberg and Sonali Paul)