Sanofi and GlaxoSmithKline (GSK) have delayed their COVID-19 vaccine programme after phase I/II results found a low immune response in older adults who received their investigational vaccine.

In a phase I/II study of Sanofi/GSK’s adjuvanted recombinant protein-based vaccine, interim results found the jab induced an immune response comparable to recovered COVID-19 patients in adults aged 18 to 49 years.

However, the results also found that the vaccine did not have the same effect in older adults, who demonstrated low immune responses – likely due to an ‘insufficient concentration of antigen’, according to the Sanofi/GSK.

The companies have now decided to plan a phase IIb study, expected to begin in February 2021, to test an improved antigen formulation which recently showed promise in a recent challenge study in non-human primates.

In this challenge study, the improved antigen formulation demonstrated protection against lung pathology and lead to rapid viral clearance from the nasal passages and lungs within two to four days.

‘These results increase the Companies confidence in the capacity of the adjuvanted recombinant platform to deliver a highly efficient vaccine for all adults,’ the companies commented in a statement issued today.

The phase IIb study, in addition to testing the improved antigen formulation, will include a proposed comparison with an authorised COVID-19 vaccine.

If the data in this mid-stage study is positive, Sanofi/GSK expect a that a phase III study could start in the second quarter of 2021.

Depending on the results in phase III, regulatory submissions could be expected in the second half of 2021, which will delay the vaccine’s potential availability from the previously anticipated mid-2021 to the end of 2021.

“The results of the study are not as we hoped. Based on previous experience and other collaborations, we are confident that GSK’s pandemic adjuvant system, when coupled with a COVID-19 antigen, can elicit a robust immune response with an acceptable reactogenicity profile,” said Roger Connor, president of GSK Vaccines.

“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,” he added.