Preliminary data from CureVac's first-generation mRNA candidate vaccine showed that it was only 47% effective at preventing any severity of COVID-19.
The company said late Wednesday that the shot, which the European Commission signed up to buy an initial 225 million doses of late last year, had failed to meet the prespecified measure of statistical success in a phase 2b/3 study.
The 40,000-subject trial, spanning Latin America and Europe and conducted with help from Bayer, will still continue on to a final analysis in "the next few weeks," and the company said the initial data has been delivered to the European Medicines Agency.
Almost to match, the price of CureVac shares tanked more than 50% in after hours trading following the news, dropping to less than $46.
The data came as a surprise following an earlier study in mice, which in March CureVac said showed promising results against the Beta variant of the coronavirus, also known as the B.1.351 mutation that first emerged in South Africa.
The latest results included 134 cases that took place at least two weeks after the vaccine's second dose was administered: 57% of the cases were from so-called variants of concern, while only one was identified as the original SARS-CoV-2 virus.
According to CureVac, the study suggested efficacy in younger participants but not for those 60 years or older.
“We are still planning for filing for approval,” CureVac CEO Franz-Werner Haas told the New York Times.
CureVac said the vaccine suggests age- and strain-dependent efficacy, as there were at least 13 variants circulating within the subset of the study population that was assessed for the initial analysis.
“While we were hoping for a stronger interim outcome, we recognize that demonstrating high efficacy in this unprecedented broad diversity of variants is challenging. As we are continuing toward the final analysis with a minimum of 80 additional cases, the overall vaccine efficacy may change,” Haas said in a statement.
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CureVac looked primed to push its shot into the European market just in the nick of time, as the bloc’s vaccination campaign suffered a number of setbacks from Johnson & Johnson and AstraZeneca's offerings.
Their European rollout has been plagued with delivery delays and safety concerns over rare but serious blood clots. Late last year, the European Commission inked a supply deal with CureVac for 225 million doses to start, with the option to secure an additional 180 million. Deliveries were supposed to begin once it was deemed safe and effective.
CureVac thought it was on track to file its mRNA vaccine with European regulators as early as last month, Haas told Reuters in early May. At the time, he said cases among trial participants were “coming in fast,” bringing the mRNA maker closer to a read-out. A month later, however, the news service reported that the European Medicines Agency likely wouldn't make a decision on CureVac’s shot before August.
And with the EU’s vaccination campaign gaining steam with shipments from Pfizer and its German partner BioNTech by that point, CureVac’s shot was floated as an option for low- to middle-income countries with lagging vaccination efforts.
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Still, CureVac said the blow to its first-generation vaccine will not stop the company from its commitment to the pandemic, and it is continuing its work with GlaxoSmithKline on a second-generation candidate aimed at the second half of 2022.
A GSK spokesperson said the mRNA backbone of the newer vaccine is different than the previous generation, which GSK has had no part in developing.
"GSK partnered with CureVac on second generation mRNA vaccine development based on preclinical data which indicate a faster, up to 10-fold increase in immunogencity vs. first generation," the spokesperson said in a statement to Fierce Biotech. "This data supports our intent to develop low-dose monovalent and multivalent vaccines to tackle emerging COVID-19 variants."