Covid-19: 'Encouraging' signs in early trial of possible Covid vaccine

Henrietta Brewer
May 24, 2020

The trial assessed the safety and ability to generate an immune response of different dosages of the new Ad5-nCoV vaccine in 108 healthy adults between the ages of 18 and 60 years who did not have SARS-CoV-2 infection. The primary endpoint of the Phase I trial was to note adverse events one week after vaccination and the patients were followed for a total of 28 days thereafter.

"These results represent an important milestone".

At the study's start, none of the patients - who had never been infected with coronavirus - had neutralizing antibodies against SARS-CoV-2, the virus that causes COVID-19.

"However, these results should be interpreted cautiously".

Many potential vaccines that appear promising in animals fail in humans, which is why we go through the expense and delay of clinical trials, but success in a fellow primate is a better indication than in more distantly related animals.

The Chinese vaccine, the first to be tested in humans, uses a weakened version of the common cold virus - an adenovirus - to deliver genetic material that codes for the SARS-C0V-2 protein to the cells. These cells then produce the spike protein and travel to the lymph nodes where the immune system makes antibodies that will recognize that spike protein and ward off the coronavirus.

"Our study provided a new vaccine platform simulating coronavirus surface protein and internal nucleic acids, therefore, combining features of inactivated vaccines and mRNA vaccines", the researchers added.

The antibody titer (the measure used for antibody levels) for both binding and neutralising antibodies was directly proportional to the dose of the vaccine.

Scientists found that all volunteers well tolerated the doses with no serious adverse events.

As per the study, about 81% of all the participants (83% in the low-dose group, 83% in the middle-dose group and 75% in the high-dose group) showed at least one adverse reaction to the vaccine within the first seven days. The most common adverse reactions were mild pain at the injection site in 54 per cent (58/108) of the recipients, fever (46 per cent, 50/108), fatigue (44 per cent, 47/108), headache (39 per cent, 42/108) and muscle pain (17 per cent, 18/108). Data the company released was limited to a handful of trial participants, so at this point it is largely unknown how effective that vaccine candidate could be, but the company was optimistic.

The side effects persisted for less than 48 hours.

More than 100 vaccine candidates against SARS-CoV-2 are in development, with about 12 in human testing created to mainly evaluate safety.

The Ad5-nCoV 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 vaccine, the authors said. "Humoral responses against SARS-CoV-2 peaked at day 28 post-vaccination in healthy adults, and rapid specific T-cell responses were noted from day 14 post-vaccination", the study stated.

The ideal vaccine would generate both antibody and T cell responses to defend against SARS-CoV-2.

The following is a brief roundup of some of the latest scientific studies on the novel coronavirus and efforts to find treatments and vaccines for COVID-19, the illness caused by the virus.

In these people, "their immune systems will essentially rear up and blunt the effect of the vaccine", said Dr. Kirsten Lyke, a vaccinologist at the University of Maryland who is leading another coronavirus vaccine trial.

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