This is the first report on a first-in-human clinical trial of a novel Ad5 vectored COVID-19 vaccine. The Ad5 vectored COVID-19 vaccine was tolerated in healthy adults in all three dose groups.

The most common adverse reactions were fever, fatigue, headache, and muscle pain with no significant difference in the incidence of adverse reactions across the groups.

Most adverse events reported were mild or moderate in severity.

We noticed a higher reactogenicity profile of the high dose at 1·5 × 1011 viral particles, presenting as severe fever, fatigue, muscle pain, or joint pain, which might be associated with viraemia caused by Ad5 vector infection.

However, the severe adverse reactions were transient and self-limiting.

Additionally, no abnormal changes in laboratory measurements were clinically significant or considered to be related to the vaccine.

The profile of adverse events reported in this trial is similar to that of another Ad5 vector-based Ebola vaccine expressing glycoprotein.

To accelerate the process of clinical evaluation of the candidate COVID-19 vaccine, we selected doses for the phase 2 study mainly on the basis of the safety profile of the candidate vaccines shown in the participants within 7 days and 14 days post-vaccination.

We chose the low dose (5 × 1010 viral particles) and middle dose (1 × 1011 viral particles) to be further assessed in a phase 2 clinical trial.

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