Patients involved in early tests of a Russian coronavirus vaccine developed antibodies with "no serious adverse events", according to research published in the medical journal The Lancet on Friday.

The so-called "Sputnik-V" vaccine produced an antibody response in everyone who participated in the early-stage trials. 

Read more: Coronavirus: Is a repeat COVID-19 infection possible?

Nevertheless, experts expressed caution, saying the trials were too small to prove safety and effectiveness.

Small step

Naor Bar-Zeev of Johns Hopkins Bloomberg School of Public Health, who was not involved in the research, said the trial results were an "encouraging but small" step. The professor added that it did not give any data on older age groups, who are significantly more vulnerable to the virus that has killed almost 900,000 people worldwide.

"Showing safety will be crucial with COVID-19 vaccines, not only for vaccine acceptance but also for trust in vaccination broadly," he said in The Lancet.

"Since vaccines are given to healthy people and, during the COVID-19 pandemic, potentially to everyone after approval following phase 3 trials, safety is paramount."

Read more: COVID-19 vaccine: From the lab to your doorstep

Concerns about speed

Russia announced last month that "Sputnik-V" had already been given the green light.

But this raised concerns among Western scientists over a lack of information, with some suggesting that moving too quickly could be dangerous.

Russia denounced the backlash as an attempt to undermine its work.

Two small groups

In the analysis, Russian researchers reported on two small groups, each involving 38 healthy adults aged between 18 and 60, who were given an immunization in two parts.

Each participant was given a dose of the first part before being given a booster 21 days later.

The volunteers were then studied carefully over 42 days and all developed antibodies within the first three weeks.

Brazil set for trials

Brazil’s Tecpar, which has signed an agreement to produce the Russian vaccine, said on Friday that it plans to conduct phase III trials on 10,000 volunteers in the South American country at the start of next year.

Jorge Callado, head of the technology institute in the southern Brazilian state of Parana, said approval for the trial will be requested of Brazil's health regulator ANVISA by the end of September and that doses will be imported for the tests.

jsi/mm (AFP, dpa, Reuters)