The setback means their vaccine launch will be held back until late next year.
Phase 1/2 study interim results showed an immune response comparable to patients who recovered from COVID-19 in adults aged 18 to 49 years, but a low immune response in older adults likely due to an insufficient concentration of the antigen.
“We are disappointed by the delay… but all our decisions are and will always be driven by science and data. We have identified the path forward and remain confident and committed to bringing a safe and efficacious COVID-19 vaccine. Following these results and the latest encouraging new preclinical data, we will now work to further optimize our candidate to achieve this goal,” said Thomas Triomphe, executive VP and head of Sanofi Pasteur on Friday [December 11].
The companies said the insufficient response in older adults seen in the Phase 1/2 study indicates the need to refine the concentration of antigen in order to provide a high-level immune response across all age groups.
The partners are now planning a Phase 2b study with an improved antigen formulation, with support from BARDA, as part of Operation Warp Speed. That trial is due to start in February 2021 and will include a comparison with an authorized COVID-19 vaccine.
The companies said that if data are positive from that trial, a global Phase 3 study could start in Q2 2021. “Positive results from this study would lead to regulatory submissions in the second half of 2021, hence delaying the vaccine’s potential availability from mid-2021 to Q4 2021.”
Roger Connor, president of GSK Vaccines, commented: “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. 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.”
Sanofi and GSK’s vaccine candidate was selected in July 2020 by US government’s Operation Warp Speed in order to accelerate its development and manufacturing.
The companies said full results of the Phase 1/2 study will be published as soon as all data are available, following a peer-reviewed publication process.
Australia abandons 'home-grown' COVID-19 vaccine candidate
Meanwhile, the Australian government has scrapped the deal it had with Australian biotech company, CSL Limited, to supply 51m doses of a COVID-19 vaccine developed by the University of Queensland (UQ), after vaccine trial participants returned false positive test results for HIV.
The response meant the antibodies produced by the vaccine could interfere with HIV diagnostic tests. However, there was no possibility the vaccine caused infection, and routine follow-up tests confirmed no HIV virus was present, said the developers.
The UQ said that, following consultation with the Australian government, CSL will not progress the vaccine candidate to Phase 2/3 clinical trials.
UQ commenced a Phase 1 trial of their COVID-19 vaccine candidate – v451 – in July 2020, to assess safety and immunogenicity in healthy volunteers. CSL was working towards taking responsibility for the Phase 2/3 clinical trial and large-scale manufacture of the vaccine, upon completion of successful trials.
The vaccine contained small fragments of an HIV protein, which helped stabilize the vaccine. Some of the participants in the Phase 1 study developed antibodies against these fragments, and these antibodies triggered false positive results on some HIV tests.
“The Phase 1 data also showed the generation of antibodies directed towards fragments of a protein (gp41), which is a component used to stabilize the vaccine. Trial participants were fully informed of the possibility of a partial immune response to this component, but it was unexpected that the levels induced would interfere with certain HIV tests,” said UQ.
“With advice from experts, CSL and UQ have worked through the implications that this issue presents to rolling out the vaccine into broad populations. It is generally agreed that significant changes would need to be made to well-established HIV testing procedures in the healthcare setting to accommodate rollout of this vaccine. Therefore, CSL and the Australian government have agreed vaccine development will not proceed to Phase 2/3 trial,” added the university.
The Australian government said it has now ordered an extra 20 million doses of the COVID-19 vaccine being developed by the University of Oxford and AstraZeneca, and 11 million more doses of the Novavax vaccine.