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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 available in Singapore are as follows:

Vaccine name Vaccination roll out date 
Pfizer-BioNTech COVID-19 vaccine 30 Dec 2020 
Moderna COVID-19 vaccine 12 Mar 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

  • A total of 4,704 suspected AE reports (0.13% of administered doses) were received, with 157 reports (0.004% of administered doses) classified as serious AEs after assessment. A total of 3,680,368 doses have been administered. Among the serious AE reports, the most frequently reported AEs were anaphylaxis and other severe allergic reactions.
  • The most commonly reported AEs were consistent with those typically observed following vaccination. They include injection site reactions such as pain and swelling (including delayed reactions also known as “COVID arm”), dizziness, fever, muscle aches and pain, headache, shortness of breath and allergic reactions (such as rash, itch, hives and swelling of eyelids, face and lips). These are also in line with the events described in the COVID-19 vaccines product information.
  • Cases of myocarditis and pericarditis (inflammation of the heart muscles and outer lining of the heart, respectively) have been reported with COVID-19 vaccines both overseas and locally. Myocarditis and pericarditis have many causes and most are due to viral infections and immunological reactions. In most cases, the inflammation is mild. We have received 6 reports of myocarditis and pericarditis, of which 4 were in males less than 30 years of age. While the local numbers are small, and within the upper end of the expected range for this age group, based on background incidence, the pattern of occurrence after Dose 2 of mRNA vaccines and in young men (between 18 and 30 years old) is consistent with what has been observed in the US and Israel so far. HSA will continue to monitor this potential safety issue closely.
  • Rare instances of anaphylaxis, a severe life-threatening allergic reaction have been linked to the COVID-19 vaccines, a known adverse reaction associated with vaccines in general. The incidence rate of anaphylaxis locally is similar to those reported overseas. Cases of Bell’s Palsy (facial muscle weakness which will generally recover completely even without treatment), an adverse event of special interest (AESI), have also been observed in some vaccine recipients. The incidence rate is within the background incidence.
  • It is important to note that heart attacks and strokes occur naturally within our population, regardless of whether people are vaccinated or not. The frequency of heart attacks and strokes in vaccinated persons locally is within the background incidence, and to date, there is no evidence that the vaccines can directly cause these events. No deaths from heart attacks, strokes or any other causes suspected to be associated with the vaccines have been reported locally.
  • 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 when warranted.

Date of publish: 11 June 2021

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


Previous reports

Publication date  HSA Safety Update Report
6 May 2021 HSA Safety Update No.1 on COVID-19 Vaccines (30 December 2020 to 18 April 2021)162 KB