90 suspected adverse events reported after Sinovac COVID-19 vaccinations in Singapore: HSA


Other serious adverse events include worsening of the underlying asthma, difficulty breathing,
fast heartbeat, rise or fall in blood pressure, chest discomfort and pain
Pericarditis or myocarditis.

Serious adverse events are closely monitored by HSA.

HSA said the occurrence of background illnesses or underlying medical conditions will be taken into account when determining whether the vaccine contributed to these events.

“Most people who have experienced serious adverse events have recovered or are recovering,” said HSA.


In the update, HSA also listed several adverse events of particular concern, including anaphylaxis, Bell’s palsy, myocarditis, and pericarditis.

An adverse event of special concern is “a medically significant event that has been observed with other vaccines in the past,” said HSA.

“HSA closely monitors the occurrence of such adverse events to detect an increase in incidence from baseline,” it said.

Cerebral vein thrombosis (CVT) was one of the adverse events of particular concern identified by HSA.

“Rare cases” of CVT with the Pfizer BioNTech and Moderna COVID-19 vaccines have been reported, both overseas and locally.

CVT is a very rare form of blood clot that occurs in the veins of the brain and can occur naturally whether or not people have been vaccinated, the agency said.

HSA has received 10 suspected CVT cases with the Pfizer-BioNTech and Moderna COVID-19 vaccines. None of the cases had a fatal outcome, it was said.

“The number of reported cases of CVT is small and with observed fluctuations in annual background incidence rates locally, it cannot be determined whether an increased incidence of CVT is associated with the use of mRNA vaccines,” said HSA, adding that it observed attentively this event and examines the cases with its expert panels.

“So far, no foreign regulatory authorities have identified CVT as a safety signal for mRNA vaccines.”

HSA said it was important to note that the locally reported CVT cases are not associated with thrombocytopenia, which is low platelet counts, and are different “in clinical presentation” from the foreign CVT cases with thrombocytopenia which with AstraZeneca and Johnson. & Johnson reported COVID-19 vaccines.

HSA added that some of the potential risk factors for CVT include a history of bleeding disorder, head trauma, and the use of medications such as oral contraceptives and hormone replacement therapy.

Patients with CVT are usually treated with anticoagulants – medicines that thin the blood – for a few months.

The annual background incidence of CVT in the general population is 1.3 to 2 per 100,000 people, HSA said.

“A local study also reported that CVT is linked to COVID-19 infection with an incidence of 8.4 per 100,000 infections,” she added.

In its update, HSA said that “most” of the 96 reported side effects of Bell’s palsy were “not serious”.

“The local incidence rate is estimated at 2.4 per 100,000 people per month, which is within the background incidence of 1.1 to 4.4 per 100,000 people per month prior to vaccination.”

It added that Bell’s palsy was reported in the clinical trials of the Pfizer BioNTech and Moderna COVID-19 vaccines, but the numbers were judged to be background incidents.

“Most patients will generally recover completely without treatment,” it said.