A coronavirus vaccine being developed by GlaxoSmithKline and its French partner, Sanofi, will be delayed until the end of next year after trials revealed it failed to produce a strong immune response in older people. The drug companies hoped to have regulatory approval for the candidate vaccine in the first half of 2021, but interim results from a phase 1/2 trial showed an “insufficient” response in the over-50s, the age group most vulnerable to severe Covid-19. The results released on Friday are a stark reminder that despite a flurry of positive results from vaccines produced by Pfizer/BioNTech, NIH/Moderna and Oxford University/AstraZeneca, developing effective vaccines at speed is no simple task. In those aged 18- to 49-years-old, the GSK/Sanofi vaccine produced an immune response similar to that seen in patients who recovered from Covid-19, but in older adults companies reported a “low immune response … likely due to an insufficient concentration of the antigen”. The antigen is the viral protein that primes the immune system to fight coronavirus. The companies will now reformulate the vaccine and launch a phase 2 trial in February with an aim to deliver approved shots in the last quarter of 2021, barring any further setbacks. Britain has pre-ordered 60m doses of the GSK/Sanofi vaccine as part of its portfolio of 355m shots from seven different vaccine developers. This week, the UK administered the first of 40m shots of the Pfizer/BioNTech vaccine. The Oxford/AstraZeneca vaccine is expected to join the mass vaccination programme but is awaiting approval from the UK regulator. Roger Connor, the president of GSK Vaccines, said the results of the study were “not as we hoped”, adding: “It is also clear that multiple vaccines will be needed to contain the pandemic. “Our aim now is to work closely with our partner Sanofi to develop this vaccine, with an improved antigen formulation, for it to make a meaningful contribution to preventing Covid-19.” Stephen Evans, a professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine, said the results highlighted why many scientists were amazed at the success of the BioNTech, Moderna and Oxford vaccines. “The first few vaccines to get to an interim analysis in phase 3 trials were unusual to have got that far without notable problems,” he said. “This shows what we know – that it is not always easy to develop a new vaccine to the point of being used to prevent the disease. Getting a vaccine that shows efficacy in the relevant age and other groups is not a straightforward path; many uncertainties can persist.” Evans said it was possible that adjustment of doses and constituents of the vaccine could improve responses in elderly people, but that it was not guaranteed. “It shows that we need to continue development of vaccines for Covid-19, because not every vaccine will get to the point of finishing phase 3 trials with demonstrated efficacy and lack of serious harm, and even those that do get there may find problems after their introduction that restrict or even prevent their widespread usage. “We are certainly not at the end of the process for vaccines against Covid-19 and there will be things that surprise us as we progress. While any delay is disappointing, it shows that vaccines are not as simple to produce as the early successes might have implied,” he said.