Between June 18 and August 3, 2020, Russian scientists enrolled 76 healthy adults aged 18 to 60 in two Phase I/2 trials. In Phase I of each study, one dose of the vaccine was administered intramuscularly with continuous monitoring for 28 days. On day 21, for Phase 2, the volunteers were given a prime-boost vaccination.
According to the study results, all participants produced antibodies to the SARS-CoV-2 glycoprotein. During Phase I of both studies, SARS-CoV-2 antibodies were detected on day 14 in 89% of those administered rAd26 and 84% in those who received rAd5. During Phase 2, antibodies were detected in 85% of volunteers on day 14 and 100% of participants on day 21. Additionally, boosting with rAd5 showed an increased in SARS-CoV-2 antibodies: 5,322 compared with 1,866 seven days post-boost vaccination.
As reported by the researchers, most adverse effects were mild with no serious side effects detected. The most common adverse effects were pain at injection site (58%), hyperthermia (50%), headache (42%), asthenia (28%), and muscle and joint pain (24%).
That being said, there were numerous limitations to the study, including the short duration of follow-up (42 days) inclusion of only male volunteers in some parts of Phase I, extremely low number of participants, and no control vaccine. Additionally, the age of the participants skewed heavily toward young persons.
This Phase 1/2 clinical study of 76 participants is what allowed the Russian government to approve the vaccine for provisional licensure in early August. And while provisional licensure does allow the vaccine to be used in some volunteers and throughout high-risk groups, it also requires a large-scale study of the general population. The researchers say the Phase 3 clinical trial, which involves 40,000 volunteers from different age and risk groups, was approved on Aug. 26, 2020 and will begin soon.
