A Chinese biotech just published the first human data for its coronavirus vaccine candidate, supporting further trials

• An experimental coronavirus vaccine developed by a Chinese biotech became the first candidate to publish human data in a medical journal.
• Researchers that tested CanSino Biologic's vaccine in 108 volunteers in Wuhan, China, published their findings Friday in The Lancet, a top medical journal.
• The scientists say the vaccine was well tolerated and that early data supports additional trials. CanSino's vaccine is now being tested in a larger, mid-stage trial.
• Nearly all volunteers developed some level of antibodies and T-cells, critical components of the immune system's response to invading pathogens. But it's not yet clear to scientists what levels of immune response are needed to protect people from infections.
• About 4 in 5 participants had some level of side effects. Nine people developed severe fevers, although the researchers said all side-effects were self-resolving and lasted no more than two days.

One of the leading coronavirus vaccine candidates showed signs of promise in an early human study that was primarily focused on safety.

The vaccine from CanSino Biologic was tested in 108 healthy volunteers at three dose strengths: low, medium and high. Researchers concluded it was tolerable and led to immune responses, supporting further clinical trials. The data was published Friday in The Lancet, a top medical journal.

It is the first published data to come from a coronavirus vaccine program. The Massachusetts biotech Moderna released a positive description of preliminary results earlier this week, but did not provide data or publish the information in a medical journal. Moderna executives said the data is in the hands of the US National Institutes of Health, which will release it at a later date.

Read more: We just got our first human results for a coronavirus vaccine. Here are the 5 biggest questions we still need answered about Moderna's injection.

CanSino is a Chinese biotech that developed the vaccine candidate with the Beijing Institute of Biotechnology. Moderna and CanSino were the first vaccine programs to start human testing in mid-March. In April, CanSino advanced to mid-stage clinical trials after reviewing preliminary data from this initial study.

The vast majority of participants — about 4 in 5 — registered some level of side effects, typically pain around the injection site (54% of participants reported), fever (46%), fatigue (44%), and headache (39%). Within a month of being vaccinated, none of the 108 volunteers had any serious adverse events, the researchers found.

Nine people did have "an episode of severe fever," the researchers noted. Five of those people were in the high-dose group, which means 14% of the high-dose group suffered from severe fever. In total, 17% of the high-dose group had some form of severe side effect.

These were still self-resolving side effects, persisting for no more than 2 days following the injection, according to the findings.

While the study was primarily geared to see if the vaccine was safe in humans, researchers also measured antibody levels in the vaccinated volunteers. Antibodies are virus-fighting proteins that play a critical role in preventing future viral infections.

Researchers tested for two types of antibodies: binding and neutralizing. While binding antibodies will grab onto the virus, they do not necessarily prevent it from infecting healthy cells and replicating. Neutralizing antibodies are the critical test for a vaccine, as these proteins can help kill the virus and prevent infection.

It remains unclear what level of neutralizing antibodies people need to fight off infection. Researchers are actively trying to figure that out by studying the antibody responses of recovered COVID-19 patients as well as testing animals such as mice, guinea pigs, and monkeys.

"Neutralising antibodies against live SARS-CoV-2 were all negative at day 0, and increased moderately at day 14, peaking at 28 days post-vaccination," the researchers wrote.

Read more: Scientists are racing to create a coronavirus vaccine that can halt the pandemic in its tracks. Here are the top 3 candidates aiming to be ready this fall.

They found the concentration of neutralizing antibodies increased along with the dose strength.

Nearly all the volunteers had significant increases in the level of binding antibodies. Nearly 60% had at least a four-fold increase in neutralizing antibodies.

The researchers also measured another critical component of the immune response: T-cells. They found detectable levels of T-cells peaking after two weeks. "High proportions of participants with positive T-cell responses were noted across all the dose groups post-vaccination," they wrote.

It remains unclear what level of antibodies and T-cells are needed to protect humans from infection.

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