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Safety updates on COVID-19 vaccines

Find out about suspected adverse events which have been reported to HSA following COVID-19 vaccination in Singapore.


HSA actively monitors the safety of COVID-19 vaccines authorised in Singapore to ensure that the benefits of these vaccines continue to outweigh the risks and that they remain safe for use. This is done through adverse events (AEs) monitoring systems to detect any potential safety signals so that relevant measures can be taken expeditiously. 

The COVID-19 vaccines currently authorised under Pandemic Special Access Route (PSAR) are as follows:

Vaccine name Vaccination roll-out date 
Pfizer-BioNTech COVID-19 vaccine 30 December 2020 
Moderna COVID-19 vaccine 12 March 2021

The following report provides an overview of suspected AEs that have been reported to HSA by healthcare professionals following the use of COVID-19 vaccines. The report also includes HSA's assessment of these reported AEs.

Summary of report (as of 31 August 2021)

Date of publish: 16 September 2021

  • A total of 8,716,085 doses of the Pfizer-BioNTech and Moderna mRNA vaccines have been administered, out of which 11,737 suspected AE reports (0.13% of administered doses) were received. Of these, 498 reports (0.006% of administered doses) were classified as serious AEs.
  • The most commonly reported AEs were consistent with those typically observed following vaccination. They include dizziness, shortness of breath, chest tightness/discomfort, palpitations, injection site reactions such as pain and swelling, fever and allergic reactions (such as rash, itch, hives and swelling of eyelids, face and lips). These typically resolve within a few days. Among the serious AE reports, the most frequently reported AEs were anaphylaxis and other severe allergic reactions.
  • In the age group of 12 to 18 years, the most commonly reported AEs include rash, hives, angioedema (swelling of the eyelids, face and lips), chest tightness/discomfort, shortness of breath, fever, dizziness and light-headedness. Syncope (fainting and temporary loss of consciousness) has also been reported, particularly in this age group, and it is generally triggered by anxiety and fear of pain during the vaccination process, rather than by the vaccines. The local incidence rate for syncope in this age group is similar to overseas reports.   
  • Rare instances of anaphylaxis, a severe life-threatening allergic reaction, have been linked to the COVID-19 vaccines. It is a known adverse reaction associated with vaccines in general. The incidence rate of anaphylaxis locally is similar to those reported overseas.
  • Rare cases of myocarditis and pericarditis have been reported with mRNA COVID-19 vaccines both overseas and locally. They are caused by inflammation of the heart muscles and outer lining of the heart, respectively. Myocarditis and pericarditis are not heart attacks, which are usually caused by blockage of the blood vessels that supply the heart. Review of the local reports showed an increased risk of myocarditis and pericarditis, particularly after Dose 2 of the vaccines. The risk is observed to be higher in young males aged 30 years and below. Most of the cases have responded well to treatment and have recovered or were discharged well from hospital. To mitigate the risk of myocarditis/pericarditis, the period of abstinence from strenuous exercise or physical activity after vaccination is extended to two weeks instead of one week. 
  • It is important to note that heart attacks and strokes occur naturally within our population, regardless of whether people are vaccinated. The frequency of heart attacks and strokes in vaccinated persons locally is within the background incidence rates, and to date, there is no evidence that the vaccines can directly cause these events.
  • Cases of Bell’s Palsy (facial muscle weakness caused by inflammation of the facial nerve) have also been observed in some vaccine recipients. Generally, patients will recover completely even without treatment. The incidence rate is within the background incidence.
  • Ninety AEs including five serious ones have been received for the Sinovac-CoronaVac COVID-19 vaccine following its placement under the Special Access Route on 2 June 2021.
  • Overall, based on the data to date, the benefits of the Pfizer-BioNTech and Moderna COVID-19 vaccines continue to outweigh the known risks in a pandemic. HSA will continue to actively monitor the safety profile of the COVID-19 vaccines and relevant regulatory actions will be taken to safeguard public health.

For more information on COVID-19 vaccination in Singapore, please refer to MOH website (