Japanese researchers have found that two out of three people experienced fatigue after their first shot of the AstraZeneca coronavirus vaccine.
A research team of the health ministry analyzed the symptoms of 179 people who received their first dose at eight medical institutions across the country since August.
Sixty-six percent felt fatigue, 51 percent had headaches, and 47 percent developed a fever of 37.5 degrees Celsius or higher.
The symptoms mostly occurred one or two days after the shot and were more common among young people.
This is the first time the government has released its survey on side effects of the AstraZeneca vaccine.
Professor Ito Suminobu at the medical school of Juntendo University heads the research team.
Ito says data from clinical trials showed that recipients of the AstraZeneca vaccine more likely experienced side effects after their first jab, while recipients of other vaccines developed symptoms more often after the second dose.
The professor says his team will continue to study side effects.
The health ministry says 28,997 people in Japan had received the AstraZeneca vaccine as of September 12, and no deaths had been reported.
One-thousand 190 people had been confirmed dead after receiving either the Pfizer-BioNTech or Moderna vaccines.
The ministry says the figure per million people was 17.2 for the Pfizer-BioNTech vaccine and 2.4 for the Moderna vaccine.
Officials say no causal link to the inoculation was established in any of those cases.