A possible vaccine against the strain of coronavirus causing the COVID-19 pandemic has seen early signs of success in China. However, we are “still a long way from a vaccine for all,” a Beijing scientist warned.

A possible vaccine against SARS-COV-2, the strain of coronavirus that causes COVID-19, has been shown to be at least partially effective, a Chinese study published Friday confirmed.

The study showed that a particular active substance triggered an immune response to the SARS-COV-2 virus in the human body. Further experiments are necessary to find out if the reaction would also prevent infection with the virus in the first place.

“These results represent an important milestone,” said Professor Wei Chen who was responsible for the study at the Beijing Institute of Biotechnology.

The study, published in medical journal Lancet, proved that the active substance Ad5-nCoV was safe and well-tolerated. The active substance is the biologically active ingredient of any drug or immunization.

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The phase 1 trial involved the substance being administered to 108 healthy volunteers in Hubei province, the original epicenter of the outbreak.

“The Ad5 vectored COVID-19 vaccine is tolerable and immunogenic at 28 days post vaccination,” the authors of the study wrote. A final evaluation will be made after six months. A double-blind study with a control group has already been started as a phase trial.

However, Wei was quick to advise “caution” on interpreting the results too optimistically.

“A promising vision for the development of COVID-19 vaccines is emerging, but we are still a long way from a vaccine that is accessible to all,” he said. The results should be interpreted “cautiously,” he added.

The Lancet estimates that around 100 potential active substances are in development worldwide, including in the UK where a huge vaccine test of over 10,000 people will begin soon.