RSV vaccine development has been fraught with setbacks for decades but the pharma industry is gearing up to bring a first inoculation to market over the next few years.
The area is a key growth opportunity for GSK, as it seeks to offset declining sales of its blockbuster lung drug Advair due to generic competition.
GSK said a Phase I/II trial with about 1,000 healthy adults aged 60-80 showed that the vaccine prompted a "robust" increase in antibodies and immune cells one month after injection, indicating a stimulated immune system.
A separate product, designed to give pregnant women the ability to confer immunity to their unborn children, led to high levels of protective neutralising antibodies in non-pregnant healthy woman taking part in a Phase I/II trial.
GSK said Phase III studies, with the potential to produce data for regulatory approval, would likely start over the coming months.
The vaccines were well-tolerated with side effects including injection-site pain and headache, GSK added.
Companies including Johnson &, Sanofi and Moderna are competing to get a vaccine approved against RSV, which globally leads to about 3 million hospital stays for children under five per year.
Swedish Orphan Biovitrum's Synagis, a monthly shot, is currently the only preventive treatment against RSV in high-risk infants. Sanofi and partner AstraZeneca are working on longer-acting nirsevimab, which could be given once per cold season to that group, if approved.
GSK is also conducting early-stage studies of an RSV vaccine for children and plans to publish results some time between Oct. 26-29 for a subgroup of children which already had some exposure to the virus.
(Reporting by Ludwig Burger. Editing by Jane Merriman)