The new trial included 1,077 healthy adults aged 18-55 years with no history of Covid-19, and took place in five UK hospitals between 23 April and 21 May 2020.
The participants either received the new Covid-19 vaccine (543 people) or the meningococcal conjugate vaccine (534 people).
All participants gave additional blood samples and underwent clinical assessments to determine if the vaccine was safe and whether it provoked an immune response. Participants were also asked to record any adverse events throughout the trial.
Fatigue and headache were the most commonly reported reactions. Other common side effects included pain at the injection site, muscle ache, malaise, chills, feeling feverish, and high temperature.
Participants taking paracetamol around their vaccination had reduced pain, chills, feeling feverish, muscle ache, headache, and malaise in the two days following vaccination.
In addition, in the 10 people who received the extra dose of the COVID-19 vaccine, side effects were less common after the second dose.
Writing in a linked Comment, Assistant Professor Naor Bar-Zeev, of Johns Hopkins Bloomberg School of Public Health, said: “These trial reports are hugely anticipated. The results of both studies augur well for phase 3 trials, where the vaccines must be tested on much larger populations of participants to assess their efficacy and safety.
“Both trials used adenovirus vectors to deliver and study the COVID-19 vaccine, an innovative and efficient means of vaccine development in the midst of a pandemic. Capable of generating humoral, cellular, and innate responses, adenovirus vectored vaccines have much potential.”