Clover nears pivotal trial of GSK-adjuvanted COVID-19 vaccine

Clover aims to make more than 1 billion doses of its COVID-19 vaccine. (Clover Biopharmaceuticals)

Clover Biopharmaceuticals is set to start a phase 2/3 clinical trial of a COVID-19 vaccine featuring an adjuvant from GlaxoSmithKline. The Chinese vaccine developer committed to starting the study later this month after reviewing data on 150 participants in a phase 1 trial.

GSK agreed to make its AS03 adjuvant available to Clover for use in a trimeric spike protein subunit vaccine in February. Clover, which has previously applied its technology to HIV and other enveloped RNA viruses, assessed the effect of combining its vaccine with AS03 or CpG 1018, another adjuvant made by Dynavax, in a phase 1 trial that enrolled adults and seniors.

Everyone who received the selected 9-µg S-Trimer dose adjuvanted with GSK’s AS03 underwent seroconversion. The seroconversion rate was 100% in the younger adults who received CpG 1018 with 30 µg of vaccine, the chosen dose for the Dynavax adjuvant. The CpG 1018-adjuvanted vaccine failed to trigger seroconversion in one of the eight seniors who received that pairing.

None of the participants experienced serious adverse events, leading Clover to commit to a phase 3 program. A phase 2/3 trial of a vaccine featuring GSK’s AS03 is set to start this month. Clover plans to initiate a separate phase 2/3 featuring Dynavax’s CpG 1018  in the first half of next year.

The timeline means Clover will enter late-phase development around the same time that the leading vaccines come to market. However, the characteristics of Clover’s vaccine mean it may play a role in the global response to COVID-19 despite ceding a big head start to other prophylactics.

Preliminary stability studies show Clover’s vaccine is stable for six months and counting under normal refrigeration conditions. The vaccine is also stable at 40 degrees Celsius for at least one month. The stability data show Clover’s vaccine can be kept in parts of the world that lack the deep-freeze capabilities needed to store Pfizer’s prophylactic and can even be distributed to areas without any cold-chain facilities. 

Clover is planning to get its vaccine to many people in those parts of the world. By advancing shots featuring different adjuvants, Clover aims to make more than 1 billion doses of its vaccine. Dynavax CEO Ryan Spencer told investors last month that Clover is developing two adjuvanted vaccines to “fully utilize their available antigen production capacity.”

The Coalition for Epidemic Preparedness Innovations, which funded the phase 1 trial, said it hopes to work with Clover to make hundreds of millions of doses of the vaccine available through the COVAX initiative it is co-leading with Gavi and the World Health Organization.