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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 are as follows:

Vaccine name Vaccination roll-out date 
Pfizer-BioNTech/Comirnaty COVID-19 vaccine 30 December 2020 
Moderna/Spikevax COVID-19 vaccine 12 March 2021
Sinovac-CoronaVac COVID-19 vaccine 18 June 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 December 2021)

Date of publish: 19 January 2022

  • A total of 11,490,023 doses of the Pfizer-BioNTech/Comirnaty and Moderna/Spikevax mRNA vaccines have been administered, out of which 14,729 suspected AE reports (0.13% of administered doses) were received. Of these, 747 reports (0.007% of administered doses) were classified as serious AEs.
  • The most commonly reported AEs were consistent with those typically observed following vaccination. They include allergic reactions (such as rash, itch, hives and swelling of eyelids, face and lips), dizziness, shortness of breath, chest tightness/discomfort, palpitations, fever and injection site reactions such as pain and swelling. 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 5 to 11 years, the reports described non-serious AEs such as hives, dizziness, fever and shortness of breath. There were no serious AEs reported for this age group.
  • 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), shortness of breath, palpitations, chest tightness/discomfort, fever, dizziness, light headedness and syncope (fainting and brief episode of loss of consciousness).
  • The AEs reported in individuals who had been administered booster doses of the mRNA vaccines were similar to the profile of AEs associated with Dose 1 and Dose 2 of the vaccines and there was no observed increase in frequency of events. These include allergic reaction such as rash, hives and angioedema (swelling of the eyelids, face and lips), chest tightness/discomfort, palpitations, increase in blood pressure, shortness of breath, fever, generalised weakness and dizziness. Ten cases of myocarditis and pericarditis have also been reported following 2.2 million booster doses.
  • Rare instances of anaphylaxis, a severe life-threatening allergic reaction, have occurred after administering the COVID-19 vaccines. It is a known adverse reaction associated with vaccines in general. The local incidence rate of anaphylaxis with mRNA vaccines is estimated at 0.88 per 100,000 doses administered and is similar to those reported overseas. So far, no anaphylaxis reports have been received for the booster doses.  
  • Rare cases of myocarditis and pericarditis have been reported with various 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. As with elsewhere, the incidence of myocarditis and pericarditis with the primary series of the mRNA vaccines is observed to be highest in young males below 30 years old. Most of the patients were reported to have recovered or are recovering. COVID-19 infection is also known to be associated with myocarditis. In one study, the extra myocarditis events in the month following vaccination was estimated to be between 1 and 10 per million persons, which is substantially lower than the 40 extra events per million persons observed following COVID-19 infection.
  • There have been rare cases of cerebral venous thrombosis (CVT) reported with the Pfizer-BioNTech/Comirnaty and Moderna/Spikevax COVID-19 vaccines, both overseas and locally. CVT is very rare and involves blood clots occurring in the veins of the brain, which can happen naturally regardless of whether people have been vaccinated. HSA’s analysis found a small increase in incidence of CVT with mRNA vaccines, which translates to about 1 additional case of CVT per million doses.  Considering that the risk of CVT after COVID-19 infection is much higher than CVT after mRNA vaccination, the benefits of vaccination continue to outweigh the small increased risk of CVT.
  • Two hundred and seventy-one suspected AEs (0.08% of doses administered) including twenty serious ones (0.006% of doses administered) were reported following the administration of 332,379 doses of Sinovac-CoronaVac COVID-19 vaccine.
  • Thirty-five suspected AEs (0.05% of doses administered) including four serious AE (0.005% of doses administered) were reported with Sinopharm COVID-19 vaccine after 75,440 doses were administered.
  • It should be noted that the type and number of reports received for different COVID-19 vaccines are not directly comparable as the vaccines have been used in the vaccination programme for different durations of time. The inactivated COVID-19 vaccines have been administered only to a very small proportion (3.5%) of the population compared to the much larger scale of deployment for the mRNA vaccines.
  • Overall, based on the data to date, the benefits of the Pfizer-BioNTech/Comirnaty, Moderna/Spikevax and Sinovac-CoronaVac COVID-19 vaccines continue to outweigh the known risks when used in a pandemic. HSA will continue to closely 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 (