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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 and rolled-out are as follows:

Vaccines Authorisation date  Vaccination roll-out date 
Pfizer-BioNTech/Comirnaty COVID-19 vaccine 14 December 2020 30 December 2020
Moderna/Spikevax COVID-19 vaccine 3 February 2021 12 March 2021
Sinovac-CoronaVac COVID-19 vaccine 23 October 2021 18 June 2021
Nuvaxovid COVID-19 vaccine 3 February 2022 18 May 2022

*Pfizer-BioNTech/Comirnaty is registered as a therapeutic product by HSA on 10 December 2021. Moderna/Spikevax, Nuvaxovid, Sinovac-CoronaVac are authorised under the Pandemic Special Access Route. 

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.

Key Updates (as of 31 May 2022)

Date of publish: 27 June 2022

i) mRNA COVID-19 Vaccines

  • The incidence rates of adverse events of interest (AESIs), namely, anaphylaxis, myocarditis (inflammation of heart muscles), pericarditis (inflammation of the outer lining of the heart) and cerebral venous thrombosis (CVT) with the mRNA vaccines have stabilized. There are no new findings since the last update in February 2022 (please refer to the previous HSA’s COVID-19 Vaccine Safety Update for details).
  • Appendicitis (inflammation of the appendix) can be caused by various factors such as infections in the digestive tract or blockage of the opening of the appendix causing it to become sore and swollen. The background incidence of appendicitis is estimated to be about 100 per 100,000 persons per year. Rare cases of appendicitis have been reported following vaccination with COVID-19 vaccines globally. Locally, twenty-one cases of appendicitis following Pfizer-BioNTech/Comirnaty COVID-19 vaccination have been reported after more than 11 million doses were administered. HSA’s analysis found a small increased incidence of appendicitis occurring within 21 days after the primary vaccination series of the Pfizer-BioNTech/Comirnaty vaccine, mainly in individuals 12 to 17 years old. This translates to 2 additional cases per 100,000 doses administered. No increased incidence of appendicitis has been observed with the booster dose of the vaccine. All the cases have been discharged after hospitalisation. Individuals who experience persistent or worsening of abdominal pain after vaccination are advised to seek prompt medical treatment.

ii) Nuvaxovid COVID-19 Vaccine

  • The vaccination programme for Nuvaxovid COVID-19 vaccine was recently rolled out on 18 May 2022, with 2,792 doses being administered as of 31 May 2022.
  • Locally, four non-serious AE reports were received, describing rash, vasculitis (inflammation of blood vessels), dizziness and chest pain. These are largely consistent with what was reported in the clinical studies and are known adverse effects associated with vaccines.
  • An AESI which we are monitoring closely is myocarditis and pericarditis. While locally no AE reports of myocarditis have been received to date, a small number of reports were observed from ongoing global clinical trials. It is important to note that COVID-19 infection is also known to be associated with myocarditis. Based on published literature, 40 extra myocarditis events per million persons were observed following COVID-19 infection. HSA’s assessment is that although the potential risk of myocarditis with Nuvaxovid COVID-19 vaccine cannot be excluded, the benefits of the vaccine continue to outweigh the risks in the Singapore context. As a precautionary measure, persons who are vaccinated with the Nuvaxovid vaccine should avoid strenuous physical activity or exercise for two weeks after vaccination to mitigate the potential risk of myocarditis. Strenuous activities refer to moderate to high intensity activities such as running, weightlifting, competitive sports and playing ball games. Light intensity activities where you can still speak without feeling out of breath such as casual walking, stretching, and housework can be continued.

iii) Sinovac-CoronoVac and Sinopharm COVID -19 Vaccines (Sinopharm is supplied via HSA's Special Access Route)

  • The incidence rates of AEs and serious AEs with Sinovac-CoronaVac and Sinopharm COVID-19 vaccines have remained stable and there are no new safety updates with the vaccines (please refer to previous HSA’s COVID-19 Vaccine Safety Update for details).
Based on the local AE reports received, most of the AEs are largely expected with vaccination and reflect what has been reported globally. Overall, based on the data to date, the benefits of the Pfizer-BioNTech/Comirnaty, Moderna/Spikevax, Nuvaxovid and Sinovac-CoronaVac COVID-19 vaccines continue to outweigh the known risks when used in a pandemic. 

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