- Sanofi and GlaxoSmithKline on Friday announced a delay for their experimental coronavirus vaccine after an early-stage clinical trial showed the shot sparked weaker immune responses than anticipated.
- While effective enough in younger adults, the shot was weaker in older participants and led to "transient but higher than expected levels" of adverse events. The partners, as a result, plan to test an improved formulation in a Phase 2b study in February and, assuming positive results, start a late-stage trial in the second half of 2021 — a roughly six to nine month delay from previous estimates.
- The news is a disappointing setback for two of the world's top vaccine makers, whose program has been promised up to $2.1 billion in funding from the U.S. government. Sanofi and GSK have been using more established vaccine technology than developers like Moderna and partners Pfizer and BioNTech, which the two had argued could lead to a more potent shot.
Much has gone right in the global push to develop a coronavirus vaccine at record speed. Two potent vaccines developed with a new type of technology could be authorized for use in the U.S. within a year of their discovery, which would be a historic scientific achievement. Others are still in late-stage testing. Setbacks, so far, have been few and far between.
Sanofi and GSK's revelation on Friday, then, comes as a sobering reminder of how difficult drug development can be, and the importance of having multiple vaccines advancing in parallel.
The news comes from a Phase 1/2 trial testing the safety and immunogenicity of Sanofi and GlaxoSmithKline's vaccine in 441 adults. Participants 18 to 49 years of age produced levels of antibodies neutralizing the coronavirus that were comparable to those seen in blood samples of recovered COVID-19 patients — a key benchmark drugmakers have used to gauge the effectiveness of their vaccines.
But levels were "insufficient" in older adults and more side effects than expected were observed, although most were mild. The rate of seroconversion, or change in detectable antibodies, in vaccinated participants, was about 90% for 18 to 49 year olds; 85% for those over 50; and only about 63% in volunteers older than 60.
The results are somewhat of a surprise, as Sanofi and GSK have been relying on a well-established technology and are experienced vaccine developers. Their shot pairs the protein-based approach utilized in Sanofi's flu vaccine FluBok with an immune-boosting adjuvant from GSK. Sanofi has spoken confidently of the program, with CEO Paul Hudson saying the company has a "higher likelihood of success" than its faster-moving peers, believing it will lead to superior results.
The companies have received a commitment for as much as $2.1 billion from the U.S. government — as much backing as any vaccine in development — to fund their work. The U.S., Europe, the U.K. and Canada have pre-ordered hundreds of millions of doses as well.
In a statement, Sanofi and GSK said the disappointing results were "likely due to an insufficient concentration of the antigen" in the vaccine. An improved formulation, however, was shown in animal tests to clear the virus from the nasal passages and lungs within 2 to 4 days, which the companies believe could lead to a "highly efficient vaccine for all adults," they said.
That will have to be proven, however, starting with a new trial — a Phase 2b study of the upgraded vaccine — in February and a late-stage study afterwards. The companies had been hoping to start a Phase 3 trial by the end of the year and seek approvals in the first half of 2021. They now expect the vaccine to be available in the fourth quarter of 2021, assuming all goes well.
Despite the success of vaccines from Pfizer and Moderna, supplies of their shots will be limited initially and several others will be needed to roll out mass immunization campaigns around the globe. Sanofi and GSK's delay, as well as mixed results from partners AstraZeneca and The University of Oxford, hamper those plans, as both of their vaccine candidates are easier to store and ship.
The setbacks also heighten pressure on the next programs, from Johnson & Johnson and Novavax, that are expected to produce Phase 3 results. Both should have data in the first quarter of 2021.
Sanofi, meanwhile, has a second vaccine in development as well through a partnership with Translate Bio, a shot based on the same type of technology used in Pfizer and Moderna's vaccines. Clinical testing has yet to begin, however.