Biotech firm ReiThera has reported that the preliminary results from the ongoing Phase I study showed that its Covid-19 vaccine candidate, GRAd-COV2, was well tolerated and induced clear immune responses in healthy subjects aged 18 to 55.

GRAd-COV2 is based on a replication-defective simian (gorilla) adenoviral vector called GRAd that encodes the full-length coronavirus spike protein, which allows the coronavirus to enter human cells.

Being carried out at Lazzaro Spallanzani National Institute for Infectious Diseases (INMI) in Rome, Italy, the study got funding from the Italian Ministry of Scientific Research and the Lazio Region.

The Phase I trial is analysing the safety and immunogenicity of GRAd-COV2 in 90 healthy volunteers divided equally into two age cohorts: 18-55 and 65-85.

Each cohort is split into three study arms of 15 volunteers who are given one of three escalating doses of the vaccine.

Volunteers are monitored over a 24-week period.

The safety and tolerability of GRAd-COV2 and selection of vaccine dose for further studies is the primary objective of the trial, and to choose a vaccine dose for further investigation in a Phase 2/3 study.

Vaccine’s ability to induce immune responses (antibodies and T cells) against SARS-CoV-2 in volunteers, is the secondary objective.

Preliminary data showed that besides being well tolerated, GRAd-COV2 also induced spike-binding antibodies and T-cell responses at all test dose levels.

ReiThera CEO Antonella Folgori said: “The initial findings have shown that the vaccine candidate is well tolerated and immunogenic against SARS-CoV-2 in younger subjects, enabling the study to advance into the next phase in elderly subjects.

“Enrolment of elderly volunteers is also proceeding well, and we look forward to reporting initial results from the overall study around year end along with our plans for larger international studies.”

The trial is now progressing to analyse the vaccine candidate in the second set of three cohorts of healthy, elderly participants aged between 65 and 85.