(Corrects paragraph 1 to "safe for her fetuses" from "effective in protecting infants from the virus"; also fixes headline to comply)

Sept 29 (Reuters) - Biotechnology company Novavax Inc said data from a mid-stage study showed that immunizing a pregnant woman with its RSV vaccine was safe for her fetus.

The trial tested the vaccine against a placebo in 50 healthy pregnant women in their third trimester.

Women who received placebo showed no significant change in their antibody levels, the company said.

(Reporting by Natalie Grover in Bengaluru; Editing by Kirti Pandey)