Efforts by the British and French drugmakers GSK and Sanofi Pasteur to produce a Covid-19 vaccine have suffered a further setback, with final clinical data on the jab and a potential launch delayed until next year as they struggle to find enough uninfected people to test it on. The two vaccine specialists announced positive preliminary results from a trial that showed the vaccine raised antibody levels against Covid by nine to 43 times when given as a single booster shot in people who had already received doses of AstraZeneca, Johnson & Johnson, Moderna or Pfizer/BioNTech vaccines, for all age groups. There were no safety concerns, according to an independent review body. It is the most comprehensive booster trial to date, said GSK and Sanofi. The vaccine has suffered repeated delays, after a dosing error early on and initial clinical trials revealed it had failed to produce a strong immune response in older people. Sanofi has developed the antigen, the substance that induces the immune system to produce antibodies against it, and GSK is contributing its adjuvant, a substance that boosts the vaccine’s immune response. The booster trial is under way in countries including the US, France and the UK, and the jab is being tested on new variants including Omicron. Separate late-stage trials of its use as a primary vaccine involve more than 10,000 volunteers aged over 18. The two companies said: “Regulatory authorities require phase III efficacy to be demonstrated in naive populations, ie participants who have never been infected by the Covid-19 virus.” Most volunteers were recruited for the phase III trial in the third quarter, at a time when the number of people infected with the virus surged globally because of the Delta variant. To generate enough data to allow the drugmakers to file their booster vaccine for regulatory approval, the trials need to continue into next year, with results expected by the end of March. They had aimed to publish them by the end of this year. “These preliminary data show we have a strong booster candidate, whatever primary vaccine you have received,” said Thomas Triomphe, the executive vice-president of Sanofi Pasteur. “While pursuing a phase III trial is a challenge in a quickly shifting pandemic environment, we look forward to seeing the results to support submissions of our booster vaccine as quickly as possible.” Roger Connor, the president of GSK Vaccines, added: “As the pandemic threat continues with the current dominant Delta variant and Omicron rapidly gaining ground, booster vaccines will continue to be needed to help protect people over time. The initial booster data are promising.” GSK, which is run by Dame Emma Walmsley, is currently undergoing a complex break-up, separating its consumer arm from its pharmaceuticals and vaccines business.