Clover's COVID-19 shot tames delta in pivotal study, delivering boost to global vaccination campaign

Clover Biopharmaceuticals’ bid to help vaccinate the world against COVID-19 has taken a big step forward. Adjuvanted protein vaccine SCB-2019 held up against a range of variants in a phase 2/3 trial, teeing Clover up to seek approval of the relatively stable jab and deliver it to the COVAX Facility.

The clinical trial enrolled 30,000 people on four continents to receive the Clover vaccine or placebo. Against all variants, vaccine efficacy clocked in at 67%. Efficacy against moderate-to-severe COVID-19 was 84%, and efficacy against severe COVID-19 and hospitalization was 100%.

Clover’s efficacy against COVID-19 of any severity varied considerably by variant. Importantly, efficacy was 79% against the highly transmissible delta variant that is dominant around the world. Efficacy fell against other variants. Against the mu variant, which accounted for one-quarter of strain-identified cases, vaccine efficacy tumbled to 59%. The study provides evidence that mu, like variants such as beta, partly escapes vaccines. People are far more likely to encounter the delta variant, though.

While the study showed how well the vaccine works against a range of variants, it provided less data on its effect in seniors. Clover said enrollment of seniors was limited by the availability of approved vaccines in the population during the study, resulting in 1.3% of participants in the SCB-2019 cohort being aged 65 years and older. All five COVID-19 cases in the age group occurred in the placebo arm.

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Half of the subjects had previously been infected with COVID-19, unlike earlier clinical trials of other vaccines that focused on seronegative participants. Efficacy was similar to in the broader population, coming in at 79% versus delta and 64% against all strains. 

Clover plans to use the results to seek conditional approval in China and the EU in the fourth quarter. A filing for emergency use listing at the World Health Organization (WHO) is planned for around the same time. Clover aims to start shipping the vaccine this year.

The WHO listing will clear SCB-2019 for provision to the COVAX Facility that is trying to improve global access to COVID-19 vaccines. Gavi, the Vaccine Alliance struck a deal for 414 million doses of the vaccine over the summer, building on an earlier agreement by its collaborator, the Coalition for Epidemic Preparedness Innovations, to fund development of the shot.

SCB-2019 may be better suited to the global vaccination campaign than existing COVID-19 vaccines are. Clover showed the vaccine is stable for at least six months under normal refrigeration conditions in preliminary tests last year. The tests also showed the vaccine is stable at 40 degrees Celsius for at least one month.