The company said it hoped to get the vaccine approved by regulators and available to patients by the end of the year.
GSK, which is facing extreme pressure in the financial markets over its perceived underperformance, has had major setbacks with its tie-up with the French drugs group as its previous attempt at a vaccine failed to work.
However, today it said all adult age groups had showed a high immune response after a single dose of its new attempt.
A global phase 3 study is expected to be started in the coming weeks.
Phase 2 included 722 volunteers and showed 95% to 100% development of antibodies following a second injection in all age groups with no safety concerns.
Phase 3 will include more than 35,000 adult participants from a broad range of countries and will assess the vaccine’s efficacy against the Wuhan and South African variants.
GSK said overall the vaccine candidate created strong neutralising antibody levels comparable to those generated by people who have naturally contracted the virus.
Its president of vaccines, Roger Connor, said: “These positive data show the potential of this protein-based adjuvanted vaccine candidate in the broader context of the pandemic, including the need to address variants and to provide for booster doses.
“We believe that this vaccine candidate can make a significant contribution to the ongoing fight against Covid 19 and will move to Phase 3 as soon as possible to meet our goal of making it available before the end of the year.”
“Our Phase 2 data confirm the potential of this vaccine to play a role in addressing this ongoing global public health crisis, as we know multiple vaccines will be needed, especially as variants continue to emerge and the need for effective and booster vaccines, which can be stored at normal temperatures, increases,” said Thomas Triomphe, head of Sanofi Pasteur.
GSK and its chief executive Emma Walmsley have come under extreme pressure from investors as its share price has fallen and it has failed to get a Covid vaccine out into the market despite setting itself up as a major vaccine maker.
Activist investor Elliott recently bought a stake in the group, leading to expectations that it will demand major changes.
Walmsley is overseeing a major restructuring of the company which has included multi-billion pound acquisitions and a plan to split the business up into two businesses: consumer medicines and pharmaceuticals.
Investors have become increasingly concerned that Walmsley, who came up through consumer products, does not have the scientific expertise to run the biopharma division, as she plans tot, post-breakup.