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Current Affairs

Adenovirus COVID-19 vaccine found safe during trial

Date: 24 May 2020 Tags: Biotechnology


A phase-1 trial using a single dose of a vaccine (Ad5-nCoV) that uses a recombinant adenovirus type-5 vector that carries the genetic material that codes for spike glycoprotein of novel coronavirus was found to be safe, well-tolerated and able to generate immune responses against the virus.



The trial was carried out on 108 participants aged 18-60 years in Wuhan, China, and had 36 participants each in the low, middle and high-dose groups. The trial did not involve randomisation of participants and did not have a control arm. 



  • The most common adverse reaction was pain at the injection site, fever, fatigue, headache and muscle pain. Most adverse reactions reported were mild or moderate in severity.

  • One participant who was given the higher dose vaccine reported severe fever, along with severe symptoms of fatigue, shortness of breath and muscle pain. However, these adverse reactions persisted for less than 48 hours. No serious adverse event was noted within 28 days post-vaccination.

  • As it was a first-in-human study of the adenovirus type-5 vectored COVID-19 vaccine, it was not designed to measure the vaccine efficacy.

  • The vaccine was found to elicit neutralising antibodies, which peaked at day 28 post-vaccination, while rapid specific T-cell responses peaked at day 14 after vaccination. The antibody response to the vaccine in the high-dose group was slightly greater than that in the middle-dose and low-dose groups.

  • 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.

  • The pre-existing immunity to adenovirus type-5 vector used in the vaccine, regardless of the vaccine doses, could reduce the immune responses to the virus and also lower the peak of the responses, particularly for neutralising antibodies immunity.

  • The high pre-existing immunity might also have a negative effect on the persistence of the vaccine-elicited immune responses.

  • The phase-2 trial will be a randomised, double-blinded and placebo-controlled trial. The trial has already been initiated to determine if the results can be replicated and to also assess the vaccine for safety up to six months after vaccination.