April 24 (Reuters) - France's Sanofi SASY.PA reported first-quarter profit that beat analysts' expectations on Thursday, boosted by strong demand for its anti-inflammatory drug Dupixent, as well as newer treatments and vaccines.

Sanofi has ramped up research and development spending in recent years, prompting the company to abandon its long-term margin targets two years ago, as it seeks to build on the success of its blockbuster drug Dupixent and develop the next wave of growth drivers.

Quarterly business operating income, excluding one-off items, rose 20.1% to 2.90 billion euros ($3.29 billion), surpassing the average analyst estimate of 2.68 billion euros.

The company reported net sales of 9.90 billion euros in the first quarter, beating the average estimate of 9.64 billion euros, according to a poll posted on the company's website.

Sales of its blockbuster asthma drug Dupixent rose 20.3% to 3.48 billion euros, compared with 3.44 billion euros expected on average by analysts. Investors are keeping a close eye on sales after Sanofi and partner Regeneron REGN.O gained U.S. approval last September for Dupixent to treat a chronic lung condition.

Sales of Beyfortus, a new treatment to protect newborns from a common respiratory virus, jumped 54.9% to 284 million euros, compared with analysts' estimate of 215 million euros.

Sales of its vaccines rose 11.4% to 1.33 billion euros, compared with estimates of 1.21 billion euros.

($1 = 0.8820 euros)

(Reporting by Manas Mishra in Bengaluru; Editing by Sherry Jacob-Phillips)

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