Phase-1 trial: Adenovirus COVID-19 vaccine found safe, induces immune responses

Grant Boone
May 24, 2020

Days after USA drugmaker Moderna announced that Phase-I trial of its Covid-19 vaccine had shown positive results, researchers on Friday reported that a vaccine developed in China appeared to be safe and might protect people from the deadly virus. The final results are to be evaluated in six months.

"These results represent an important milestone". The results should be interpreted "cautiously", he added.

These are the first published phase-one results - although other companies working on vaccines are also advancing in the various trial phases. It utilizes a weakened common cold virus to convey genetic material that codes for the SARS-CoV-2 spike protein to the cells. The idea is that a person's immune system will create antibodies against the spike protein, which will help fight off the coronavirus if the person is later exposed to it.

108 healthy adults aged between 18 and 60 years were sequentially enrolled in the study.

Healthy adult volunteers in Wuhan, China, received a single intramuscular injection of either a low, middle or high dose of the vaccine. Randomized placebo-controlled studies are needed to clarify the risks and benefits of the decades-old drug in the treatment of COVID-19, the researchers said. These are the body's humoral response', which is the part of the immune system that produces antibodies to fight infection, and the "cell-mediated' arm, which depends on a group of T cells to fight the virus, the scientists said". "Moreover, animals that had higher antibody levels had lower levels of the virus, a finding that suggests neutralizing antibodies may be a reliable marker of protection and may prove useful as a benchmark in clinical testing of SARS-CoV-2 vaccines".

There were side effects - primarily pain, muscle aches and fever - but they subsided within 28 days, and no serious or unsafe side effects were reported.

The researchers tested three doses and said the highest dose seemed to be the most effective.

More than 80 percent did have some side effects, but these were mostly mild or moderate, like muscle aches, fever and pain.

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Within two weeks of vaccination, all dose levels of the vaccine triggered some level of immune response in the form of binding antibodies (that can bind to the coronavirus but do not necessarily attack it - low-dose group 16/36, 44%; medium dose 18/36, 50%; high dose 22/36, 61%), and some participants had detectable neutralising antibodies against SARS-CoV-2 (low-dose group 10/36, 28%; medium dose 11/36, 31%; high dose 15/36, 42%).

Participants blood levels of neutralizing antibodies reached their peak by the 28th day after they were injected.

Nine people in the low-dose group, two in the middle-dose and five in the high-dose group had a grade 3 high fever with an ancillary temperature (checked in armpits) above 38.5°C.

The vaccine also stimulated a rapid T cell response in the majority of volunteers, which was greater in those given the higher- and middle-doses of the vaccine, with levels peaking at 14 days after vaccination.

Within two weeks, participants in all three dosage groups had 'rapid binding antibody responses, ' meaning they showed signs that they were making antibodies capable of fighting coronavirus infection.

However, they said high pre-existing immunity to adenovirus type 5 - the common cold virus vector used in the study, may have reduced both the antibody and T-cell response in the participants.

The second study showed that that macaques recovered from COVID-19 and developed "natural protective immunity against re-infection with the virus".

The study's authors also noted that their research is limited because of its small sample size and short duration, and it also lacked a control group.

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