London, Sep 4 (IANS): A Russian Covid-19 vaccine has shown no serious side effects and elicited an immune response in early human trials, said a study published in The Lancet on Friday.

Russia last month registered the "Sputnik V", becoming the first country to approve a Covid-19 vaccine.

However, the country faced criticism for approving a vaccine before completion of Phase-3 trials.

According to the study, published in The Lancet, the researchers enrolled 76 healthy adult volunteers (aged 18-60 years) for the two Phase-1 and Phase-2 studies -- 38 people in each study.

In Phase-1 of the study, two groups of nine volunteers received one dose of either recombinant adenovirus type 26 (rAd26) vector or recombinant adenovirus type 5 (rAd5) vector, both carrying the gene for SARS-CoV-2 spike glycoprotein (rAd26-S and rAd5-S), in frozen form.

In Phase-2, another group of 20 healthy adult volunteers in each study received sequential doses of rAd26-S followed by rAd5-S of one of the two formulations.

Adverse events were mostly mild, with the most common adverse events being pain at the injection site, hyperthermia, headache, asthenia, and muscle and joint pain, said the study.

Both formulations of the vaccine were immunogenic in all participants, inducing neutralising humoral and cell-mediated responses, said the study.

In Phase-2, 85 per cent of participants had detectable antibodies at 14 days after the priming dose, rising to 100 per cent by day 21, the results showed.

"The two 42-day trials - including 38 healthy adults each - did not find any serious adverse effects among participants, and confirmed that the vaccine candidates elicit an antibody response," the study's authors wrote.

The study's authors also held that large, long-term trials, including a placebo comparison, and further monitoring are needed to establish the long-term safety and effectiveness of the vaccine for preventing Covid-19 infection.

Reports suggest that Russia is planning a Phase-3 trial of the vaccine involving 40,000 people.