Dang Duc Anh, director of the institute, on Monday said around 26 percent of those vaccinated against Covid-19 globally experience normal side effects, and that around 0.7 percent would experience severe reactions. In Vietnam, the rate of people with severe side effects is about 0.1 percent.

"There is always a certain chance of experiencing side effects following the injection. That chance is within the expected level as determined by vaccine producers, World Health Organization (WHO) and other relevant entities," he stressed.

According to the WHO, up to 10 percent of those who are vaccinated against Covid-19 experience common side effects like swelling and pain at the site of injection, headaches, nausea, joint pain or light fever. More serious effects include anaphylaxis.

Vietnam started its Covid-19 vaccination program last week, giving frontline workers their first shots of a vaccine produced by British-Swedish firm AstraZeneca and Oxford University.

Of over 11,000 people who have received their shots, 11 cases have experienced severe side effects with signs including high fever and blood pressure. Cases suffering the most severe side effects are detected sporadically and hold no obvious connections. All have been screened prior to their injections and showcased no serious underlying conditions. Their health is now stable and carefully monitored, Duc Anh said.

The causes of such side effects are being investigated by the Ministry of Health.

None have experienced blood clots after vaccination, a problem that has prompted at least 10 countries, including Denmark, Iceland and Norway to temporarily suspend the use of the vaccine, which has been approved for use in over 70 countries and territories.

AstraZeneca and European Medicines Agency have said there has been no evidence to prove the vaccine caused blood clots, and stressed its benefits far outweigh the risk of contracting Covid-19.

Over 117,600 shots of AstraZeneca vaccine have been delivered to Vietnam, expected to be depleted within this month.