Clover Biopharmaceuticals has begun a Phase II clinical trial to assess its Covid-19 vaccine candidate, SCB-2019 (CpG 1018/Alum), as a heterologous booster shot in people who received an initial vaccine regimen.

Using its Trimer-Tag technology platform, the company developed the SCB-2019 antigen, which was merged with CpG 1018 advanced adjuvant of Dynavax and aluminum hydroxide (alum).

The double-blind, controlled, randomised, two-stage trial is sponsored by the Instituto D’Or de Pesquisa e Ensino (IDOR) and has received funding from the Bill & Melinda Gates Foundation.

It is also being backed by the Brazilian Ministry of Health.

The investigator-led trial will assess the safety and immunogenicity of a booster dose of the protein-based vaccine in almost 520 healthy adult subjects at multiple trial centres in Brazil.

Its first stage will analyse three vaccine formulations given as a booster shot almost six months after the initial vaccine regimen with AstraZeneca-Fiocruz’s recombinant Covid-19 shot.

In the second stage, the immunogenicity and safety of a booster dose of the opted formulation of SCB-2019 will be analysed in people inoculated with two shots of either the CoronaVac vaccine or the AstraZeneca-Fiocruz vaccine.

The preliminary results from the trial are expected to be announced in the first half of next year.

Clover Biopharmaceuticals CEO Joshua Liang said: “We are excited to learn how our Covid-19 vaccine candidate performs as a booster dose for people previously vaccinated with either inactivated or adenovirus-vectored Covid-19 vaccines.

“SPECTRA trial data reported in September showed that vaccination with SCB-2019 (CpG 1018/Alum) in individuals previously infected by SARS-CoV-2 demonstrated a rapid and strong boosting effect on neutralising antibody titers, as well as a favourable safety profile, thus supporting the evaluation of our Covid-19 vaccine candidate as a potential booster vaccine.”

In June, Clover signed an advance purchase agreement with Gavi, the Vaccine Alliance, to deliver up to 414 million doses of the vaccine.