(Reuters) -Moderna said on Wednesday it has entered into an agreement with private equity firm Blackstone's life science investment platform for a funding of $750 million to develop its mRNA flu vaccines.

The biotech firm has been developing multiple vaccines to make up for a decline in sales of its COVID shots, sold under brand name Spikevax, and plans to spend about $4.5 billion in 2024 towards research and development.

Developing multiple vaccines "requires substantial investment in late-stage studies and we are excited to welcome Blackstone and their innovative financing model," CEO Stéphane Bancel said in a statement.

Blackstone Life Sciences will get commercial milestone payments and low-single digit royalties as part of the agreement, the COVID-19 vaccine maker said.

Shares of Moderna rose over 2% in premarket trading.

Moderna's flu shots have generated a stronger immune response against all four A and B strains of the influenza virus compared to traditional flu shots in a late-stage trial, according to data released in September.

The company estimates flu vaccines to represent an about $7 billion market this year, and expects its scope to widen as new shots become available. Moderna plans to file its application with regulators this year.

Besides the flu shots, Moderna is also developing a vaccine to prevent infections from respiratory syncytial virus (RSV), a combination shot against flu and COVID-19, a second generation COVID vaccine, and a cancer vaccine co-developed with Merck.

Its RSV vaccine is expected to be launched this year in the United States.

(Reporting by Leroy Leo and Sneha S.K. in Bengaluru; Editing by Shinjini Ganguli)