(Reuters) - French drug maker Sanofi on Friday posted stronger earnings growth than analysts had expected in the third quarter, helped by earlier-than-anticipated sales of seasonal vaccines.

Quarterly business operating income, excluding one-off items, rose by 14.4% to 4.6 billion euros ($5.0 billion), surpassing the average analyst estimate of 4 billion euros in a poll posted on the company's website.

Vaccines sales rose a currency-adjusted 25.5% to 3.8 billion euros in the quarter, ahead of a 3.2 billion euro analyst consensus.

The French drugmaker said this was boosted by earlier prescriptions for flu shots and for Beyfortus, a drug to protect infants from a common respiratory virus.

(Reporting by Ludwig Burger, editing by Tassilo Hummel)