Mike Ryan, head of the WHO's emergencies programme, welcomed news that AstraZeneca's experimental vaccine developed with Britain's Oxford University was safe and produced an immune response in early-stage clinical trials in healthy volunteers.
The results showed that the vaccine stimulated two key parts of the body's immune system - antibodies and T-cells.
However, it warned of the trial, which had 1,077 participants aged between 18 and 55: "Current results focus on immune response measured in the laboratory".
The news has been welcomed by many, including British Health Secretary Matt Hancock, who tweeted that the United Kingdom had "already ordered 100 million doses of this vaccine, should it succeed".
"The early stage trial finds that the vaccine is safe, causes few side effects, and induces strong immune responses in both parts of the immune system", the Oxford researchers said.
"Preliminary data indicates that our mRNA-based vaccine was able to stimulate antibody and T-cell responses at remarkably low dose levels", said Türeci.
"We're really pleased with the results published today as we're seeing both neutralising antibodies and T-cells", Prof.
Co-author, Professor Sarah Gilbert, cautions that more work needs to be done, and that "we still do not know how strong an immune response we need to provoke to effectively protect against SARS-CoV-2 infection". University of Oxford has been working on vaccines on MERS (Middle East Respiratory Syndrome) and Severe Acute Respiratory Syndrome (SARS) diseases, which are caused by coronaviruses.
More than 150 potential coronavirus vaccines are in various stages of development around the world, with 23 candidates already being tested in people, according to the World Health Organization. "I am very proud of what they have achieved so far".
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It is not yet known how long immunity from Covid-19 lasts, but the vaccine developers say this does not mean their jab will not provide long-term immunity.
The Oxford shot elicited neutralizing antibodies after a single dose, Hill said. While the test doesn't prove the vaccine will work, "I think we're a bit more confident it should work this week than last week".
He added it was possible that there would be vaccines available by the end of the year.
There are 23 Covid-19 vaccines now in clinical trials worldwide, according to the World Health Organization.
He said that larger trials evaluating the vaccine's effectiveness, involving about 10,000 people in the U.K.as well as participants in South Africa and Brazil are still underway.
Other vaccine trials in the US and China have had similarly promising results in early tests, but widespread distribution of an approved vaccine is likely a ways off.
The vaccine is being developed in partnership with drug company Astra Zeneca, which has already purchased 100 million doses of it, despite it not even being out of trials yet.
The authors note a number of limitations to their study, saying more research is needed to confirm their findings in different groups of people, including older age groups, those with other health conditions, and in ethnically and geographically diverse populations.
In a statement, the British government said it had secured access to a vaccine candidate being developed by Pfizer and BioNTech, in addition to another experimental vaccine researched by Valneva.