Novavax Inc said its vaccine to treat a virus that causes respiratory tract infections met the main goal, of immunizing women of childbearing age, in a mid-stage trial.
The company's shares were up 8.5 percent at $2.35 in extended trading.
The vaccine against respiratory syncytial virus (RSV) could induce immune responses at levels that can protect infants through a transfer of antibodies from the mother, Novavax said citing trial data.
The vaccine was well-tolerated, with a safety profile similar to its early-stage trial.
The trial on 330 women tested 60 microgram and 90 microgram doses of the vaccine, with and without an adjuvant — an agent to boost immune response. The women received either one or two injections of a single dose of the vaccine, or a placebo. The adjuvant showed a greater response in both regimens.
"The study was dose confirmatory at 60 micrograms. They will go with an adjuvant and will probably go forward testing two doses administered a month apart, because the greatest response was with using a two-dose regimen," MLV & Co analyst George Zavoico told Reuters.
Zavoico said the vaccine was ahead of rivals in development.
Novartis and GenVec Inc are also testing RSV vaccines in pre-clinical studies.
Novavax would have to do reproductive toxicity tests in animals before test the vaccine on pregnant women, Zavoico said.
The company is also testing the vaccine in an early-stage study with elderly patients.
"With the robust response in this trial, I believe that they will see a response in the elderly as well," Zavoico said.
(Reporting By Vrinda Manocha in Bangalore; Editing by Sreejiraj Eluvangal and Joyjeet Das)