The first participant is reported to be in good health with no safety concerns after being injected on 19 June. A second booster dose will be administered within four weeks.
About 300 volunteers are taking part in the study, which is the second coronavirus vaccine trial on humans underway in the UK.
Researchers at the University of Oxford began testing their vaccine candidate on people in April, and have enrolled more than 1,000 participants.
Fifteen healthy volunteers are expected to receive their first dose in the coming days as part of the initial phase of the Imperial trial.
Professor Robin Shattock, from the university’s department of infectious disease, said: “We now eagerly await rapid recruitment to the trial so that we can assess both the safety of the vaccine and its ability to produce neutralising antibodies which would indicate an effective response against Covid-19.
“I look forward to our progress in the coming months.”
To assess safety as well as to find the optimal dosage, the researchers are starting with a low dose and gradually increasing it to higher doses for subsequent volunteers.
Imperial’s RNA vaccine uses synthetic strands of genetic code based on the genetic material of Sars-CoV-2, the coronavirus that causes Covid-19.
It works by delivering genetic instructions to muscle cells to make the “spike” protein on the surface of Sars-CoV-2. The presence of this protein provokes an immune response, offering protection against the virus.
If the vaccine is safe and shows promising immune response, a further trial involving 6,000 people is expected to go ahead in October.
Volunteers receive first doses of experimental vaccine
Volunteers in Brazil have begun to receive injections of an experimental coronavirus vaccine developed by researchers at Oxford University, AFP reports.
The vaccine, developed together with pharmaceuticals group AstraZeneca, is one of dozens that researchers worldwide are racing to test and bring to market.
Known as ChAdOx1 nCoV-19, it is already being tested in volunteers in Britain, and was due to start being administered this week in South Africa as well.
The Federal University of Sao Paulo (UNIFESP), which is coordinating the study in Brazil, said in a statement its researchers had begun issuing the first doses on Tuesday to health workers, including doctors, nurses and ambulance drivers, who were deemed to be likely to come into contact with the Sars-CoV-2 virus.
Researchers “began triaging volunteers [on] Saturday ... following the protocols established for the study. Participants must test negative for Sars-CoV-2, the virus that causes Covid-19,” the university said in a statement.
“Starting Tuesday, volunteers with a negative blood test were administered the vaccine.”
Volunteers must be between 18 and 55 years old and work “on the frontline” of the pandemic at the Sao Paulo-UNIFESP hospital, it said.
The vaccine will be administered to 2,000 volunteers in Brazil, while more than 4,000 participants are enrolled in the clinical trial in Britain, with another 10,000 due to be recruited, according to Oxford.
Brazil was selected because it is one of the countries where the virus is spreading fastest. It has the second-highest caseload and death toll worldwide after the United States, with more than 1.1 million people infected and 52,000 killed so far.
Brazil’s acting health minister, Eduardo Pazuello, said on Tuesday the country was close to signing a contract to produce the vaccine domestically.