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An experimental Covid-19 vaccine that is being developed by US biotech firm Moderna induced antibody responses against the coronavirus in all 45 participants of a human trial, a paper published Tuesday showed.
Moderna had previously published "interim results" from its Phase 1 in the form of a press release on its website in May, which revealed the vaccine had generated immune responses in eight patients.
Though these were called "encouraging" by Anthony Fauci, the top US infectious diseases official, the full study had been eagerly awaited by the scientific community.
The company has since moved to the next stage of its trial, involving 600 people.
The new paper was published in the New England Journal of Medicine.
The 45 participants were split into three groups of 15 each to test doses of 25 micrograms, 100 micrograms and 250 micrograms.
They were given a second dose 28 days later.
After the first round, antibody levels were found to be higher with higher level doses, and after the second round, participants had higher levels of antibodies than most patients who have Covid-19 and gone on to generate their own antibodies.
More than half the participants experienced mild or moderate side-effects, though these did not rise to the level where the trial would be called off.
The side effects included fatigue, chills, headache, bodyache, and pain at the injection site.
Three participants did not receive their second dose, including one in the 25 microgram group who developed a skin rash on both legs, and two (one in the 25 microgram group, one in 250 group) who missed their window because they had Covid-19 symptoms, but their tests later returned negative.
Andrew Freedman, an infectious disease expert at the University of Cardiff who was not involved in the study, said the paper suggested the vaccine "is able to stimulate antibody production in a dose-dependent fashion."
"Importantly, the antibodies generated were able to neutralise the virus" in lab conditions, he added.
"The side effects experienced by more than half the participants are quite common after other vaccinations, although the 'more severe adverse events' experienced by three of the subjects given the highest dose may mean that dose is too high to take forward," he said.
The Moderna vaccine belongs to a new class of vaccine that uses genetic material, in the form of RNA, to encode the information needed to grow the virus' spike protein inside the human body, in order to trigger an immune response.
The spike protein is a part of the virus it uses to invade human cells, but by itself is relatively harmless.