An employee at the factory of British pharmaceutical company GlaxoSmithKline in Wavre on February 8, 2021, where the Covid-19 vaccine will be produced. Photo: AFP / Kenzo Tribouillard

British drugs giant GlaxoSmithKline and South Korean peer SK bioscience have started final stage trials of a Covid-19 jab after positive early results, they announced Tuesday.

The vaccine is facing a Phase 3 clinical trial to assess its “safety and immunogenicity” when compared with AstraZeneca’s Covid vaccine, the two companies said in a joint statement.

GSK is still trailing in the wake of Anglo-Swedish rival AstraZeneca, which rapidly developed a successful jab alongside Oxford University despite having little prior experience in vaccine development.

The new jab combines SK bioscience’s Covid vaccine candidate GBP510 with Glaxo’s pandemic adjuvant that bolsters the immune response.

“The advance to Phase 3 study follows positive interim Phase 1/2 data which showed that all participants who received the adjuvanted vaccine candidate developed strong neutralizing antibody responses,” the pair said Tuesday.

Those responses demonstrated a rate of seroconversion – or production of antibodies – of 100%, they added.

No safety concerns have so far been identified in the study.

The vaccine is then expected to be supplied via Covax – the distributor backed by the World Health Organization and the Gavi vaccine alliance – subject to positive results and regulatory approvals. 

“While many countries have made good progress with vaccination, there remains a need for accessible and affordable Covid-19 vaccines to ensure equitable access and to protect people across the world,” said GSK chief global health officer Thomas Breuer.

“We are pleased to contribute with GSK’s pandemic adjuvant and to be working with SK to deliver the vaccine at scale via Covax if it is approved.”

Results from the Phase 3 trial, which will enroll 4,000 participants from various nations, are expected in the first half of next year.

This will be the first Phase 3 study to compare outcomes of two different Covid-19 vaccine candidates.

SK has received funding from the Coalition for Epidemic Preparedness Initiative and the Bill & Melinda Gates Foundation to help it develop a low-cost jab.

“Taking this important step towards overcoming the global pandemic situation, SK and GSK will bring our technical expertise together for the development of an adjuvanted protein-based vaccine candidate, GBP510,” noted SK chief executive Jaeyong Ahn.

Glaxo is also working with French pharmaceutical giant Sanofi on final Phase 3 tests of a different Covid vaccine, which they hope to launch by the end of this year.

Phase 2 trials of that jab have already shown a strong immune response after a single shot in participants who had previously contracted the coronavirus.

GSK is also working on another two separate vaccine projects, one with Canada’s Medicago and another with Germany’s CureVac.