GlaxoSmithKline, Medicago hit 75% efficacy against delta COVID strain, but omicron muddies waters

COVID-19 vaccine
(Getty/Hector Pertuz)

GlaxoSmithKline and partner Medicago have seen some strong efficacy numbers against the current dominating SARS-CoV-02 strain delta, but the emergence of omicron will likely upset these numbers.

Let’s look at the data we do have: GSK and Medicago, which partnered up last year, have released phase 3 data from their plant-derived adjuvanted COVID-19 vaccine candidate CoVLP+AS03, which in recent midstage tests showed it was somewhat differentiated from other vaccines through the mixed cellular response it triggers.

The vaccine consists of self-assembling viruslike particles (VLPs) that display trimers of the recombinant S protein from SARS-CoV-2. Medicago has paired the VLPs, which it makes in Nicotiana benthamiana, a close relative of tobacco, with GSK’s oil-in-water adjuvant system AS03 to initiate an innate immune response that supports the subsequent adaptive immune response to the vaccine.

Today, the pair has released positive efficacy and safety results from the global phase 3 placebo-controlled test across 24,000 subjects and, for the first time, they have been linked with the now dominate and highly transmissible strain delta.  

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GSK said vaccine efficacy was shown in an environment “dominated by SARS-CoV-2 variants, unlike most published phase 3 efficacy trials for currently licensed COVID-19 vaccines that were conducted when only the ancestral virus was circulating, making direct comparisons impossible.”

That caveat comes as the numbers are not in the mid-90s as they have been for mRNA vaccines when first tested in phase trials last year, but we do know that delta may have an impact on the efficacy of all vaccines.

With that in mind, the pair found that the overall vaccine efficacy rate against all variants of SARS-CoV-2 was 71%, with the number for people with an initial seronegative status (showing no previous exposure to COVID-19), was 75.6%. The vaccine works as two doses of 3.75 µg of antigen combined with GSK's pandemic adjuvant given 21 days apart.

Possibly the most important numbers were for the delta variant, now the dominant global variant of the virus, for which the vaccine showed efficacy of 75.3% against COVID-19 of any severity. Efficacy was 88.6% against the gamma variant, though it's in small numbers of people.

No cases of the alpha, lambda and mu variants were observed in the vaccinated  group, while 12 cases were observed in the placebo group. Most importantly, however, was that no omicron variants were tested, as it was not in existence during the study.

This new variant, with a whole host of mutations not seen before that has scared the life out of some virologists, appears to be spreading exponentially and at a faster rate than ever seen before in South Africa, one of the first places the virus was identified, and there are fears that its evolution could dilute the effect of vaccines.

This holds true not just for GSK-Medicago, but all the current vaccine makers: AstraZeneca, Pfizer-BioNTech, Moderna and others working on new vaccines including CureVac, Sanofi, Valneva, Novavax and more.

Just how well any of these vaccines work against omicron, predicted to become the globally dominate strain in a matter of months if its transmissibility is as high as feared, will now become the main focus of COVID R&D.

Full results of GSK/Medicago’s phase 3 study “will be released in a peer-reviewed publication as soon as possible,” but as so often with COVID vaccine development, it may be answering questions we no longer need to know the answer to, and unable to answer the one we do: How will it stand up to omicron?

Still, the pair is hopeful it can have its place, and said that, based on these results, Medicago will “imminently seek regulatory approval from Health Canada as part of its rolling submission.”

“These are encouraging results given data were obtained in an environment with no ancestral virus circulating,” said Thomas Breuer, GSK’s global COVID-19 adjuvanted vaccines lead and chief global health officer.

“The global COVID-19 pandemic is continuing to show new facets with the current dominance of the delta variant, upcoming omicron, and other variants likely to follow. The combination of GSK’s established pandemic adjuvant with Medicago’s plant-based vaccine technology has significant potential to be an effective, refrigerator-stable option to help protect people against SARS-CoV-2.”