By Alishah Khan, Edited by Sami Morse and Kathleen Navas
CanSino Biologics, a vaccine development company based in Tianjin, China, has been working on developing a SARS-CoV-2 vaccine since March of 2020. The vaccine is based on adenovirus type 5 (Ad5), a virus commonly used in vaccines and a weakened version of the virus associated with the common cold. CanSino’s vector encodes SARS-CoV-2’s spike protein, the tool with which the novel coronavirus enters human cells; theoretically, a patient would be injected with this vaccine, easily kill the weakened, modified Ad5 virus--unable to replicate in its host, and, subsequently, create long-lived immunity towards the SARS-CoV-2 spike protein that the coronavirus is producing.
In May, CanSino’s results from its Phase 1 clinical trials were published. Researchers determined that CanSino’s vaccine was immunogenic, citing post-vaccination increases in antibodies and T cells specific for SARS-CoV-2 spike protein, and safe, noting that there were no adverse events noted after vaccine administration, though patients did experience mild to moderate reactions, such as fever, fatigue, and headache.
Phase 2 trials for the CanSino Biologics vaccine began this April, with the aim of becoming the first vaccine available for public use. Initial testing occurred on a group of about 500 individuals with two different dosages, at 5 x 1010 and 1 x 1011 viral particles. All testing was double-blind and placebo-controlled, meaning that placebos were given out, but neither the researchers nor the participants knew whether participants were receiving a placebo or the true vaccine. Average age of participants was 39.7 years old, with all participants being over the age of 18 and healthy. Although no serious safety concerns were linked to the results of the test, 72% of participants noticed at least one “adverse effect”, such as fatigue (42% in the higher dose group, 34% in the lower dose group), fever (32% in the higher dose group, 16% in the lower dose group), or headache (29% in the higher dose group, 28% in the lower dose group). These are common symptoms after receiving most common-cold-related vaccinations. Researchers determined that both dosages were immunogenic (evoked an antibody response to SARS-CoV-2 spike protein) and non-harmful, with the lower dosage eliciting a lower percentage of mild adverse effects.
Recruiting over 40,000 participants, phase 3 clinical trials began in August and are currently ongoing in Saudi Arabia, Pakistan, and Russia. These studies will more broadly and intensely measure the safety, immunogenicity, and efficacy of the Ad5-nCoV vaccine.
Prior to the publication of the phase 2 trial results in July, the Chinese military approved use of the vaccine among its members on June 25th, being the first to do so. Important to note, there is some concern regarding Ad5 vaccine vectors and a potential for increased susceptibility to HIV-1 acquisition among males who may receive the vaccine. Also, vaccine vectors may be harmful to immunocompromised individuals, as they have a chance to reactivate. These are important concerns to keep in mind, as the vaccine finishes up its phase 3 clinical trials and looks to reach the general public.
Results from ongoing research and the current understanding of COVID-19 are constantly evolving. This post contains information that was last updated on October 28, 2020.