SINGAPORE — A total of 157 suspected serious “adverse events” have been reported out of nearly 3.7 million doses of the Covid-19 vaccines that have been administered in Singapore as of May 23, the Health Sciences Authority (HSA) said.

In an update late on Friday (June 11) night, HSA said that the number of suspected serious adverse events comprises 0.004 per cent of the total number of doses given so far.

The 157 suspected serious adverse events were part of the 4,704 suspected adverse events reports that the HSA had received as of May 23. This translates to 0.13 per cent of administered doses. 

Both percentages are consistent with the percentages that had been reported by the authority earlier last month. 

Reactions are classified as serious or severe if they result in hospitalisation, disability or a life-threatening illness, among other reasons.

Among the serious reports, HSA said that the most frequently reported adverse events were anaphylaxis and other severe allergic reactions.

Anaphylaxis is when someone experiences two or more of the following symptoms: Hives or swelling in the face, eyelids, lips or throat, difficulty breathing and dizziness.

“There were 26 reports of anaphylaxis and 23 reports of severe allergic reactions.

"Other serious adverse events include breathing difficulty, fast heart rate, an increase or decrease in blood pressure, chest discomfort and pain, syncope (fainting), limb numbness, weakness or pain, changes in vision, increase in liver enzymes, joint pain, seizures (fits), tinnitus (ringing in the ears) and infections.

“These serious adverse events are being closely monitored by HSA,” it said.

Among those who had developed serious adverse events, most have recovered or are recovering.

HSA noted that about 68 per cent of adverse events were reported among people who were below 60 years old.

It added that in the clinical trials of both the Pfizer-BioNTech and Moderna vaccines, people younger than 60 tend to experience more “reactogenic adverse effects” than those aged 60 and above.

“Generally, younger individuals have more active immune responses and may experience more adverse effects to the vaccines…  About 64 per cent of the adverse effects were reported in females.” 

No deaths have been linked to the jabs, HSA stressed, referring to the Pfizer-BioNTech and Moderna vaccines that are used in Singapore.

It also noted that there have been no increased frequency of heart attacks or strokes among those who have been vaccinated.

“It is important to note that heart attacks and strokes can occur naturally within our population, regardless of whether people are vaccinated or not.

“Due to the large numbers of people being vaccinated, it is expected that, by chance, some individuals may experience other medical events such as heart attacks and strokes in the days or weeks after vaccination, which may not be related to the vaccination.” 

COMMONLY REPORTED ADVERSE EVENTS

HSA noted that the most commonly reported adverse events are consistent with those typically observed following vaccination.

These include injection site reactions such as pain and swelling, dizziness, fever, muscle aches, headache, shortness of breath and allergic reactions such as rash, itch, hives and swelling of eyelids, face and lips.

These adverse events are typically resolved within a few days, it said, adding that they are in line with the events described in the Covid-19 vaccines product information and those reported overseas.

ADVERSE EVENTS OF SPECIAL INTEREST

Of note, HSA said that anaphylaxis and Bell’s palsy are examples of “adverse events of special interest” that have been observed historically with other vaccines.

Giving a further breakdown on the 26 anaphylaxis cases that have been reported, HSA said that all of the patients recovered after medical treatment.

The incidence rate of anaphylaxis reported in Singapore with the Pfizer-BioNTech and Moderna vaccines is about 0.85 cases for every 100,000 doses of the jabs administered.

This is compared to the 1.4 cases of anaphylaxis for every 100,000 doses of the Covid-19 vaccine reported last month.

HSA on Friday said that the figure is similar to the incidence rates for Moderna and Pfizer-BioNTech vaccines that were reported overseas.

Separately, 45 cases of Bell’s palsy have been reported here. It causes temporary weakness or paralysis of facial muscles and patients often recover completely from this without the need for treatment.

“The local incidence rate is estimated to be 3.35 (cases for every) 100,000 persons per month, which is within the background incidence of 1.1 to 4.4 per 100,000 persons per month prior to the introduction of vaccination,” HSA said.

The incidence rate of 3.45 per 100,000 persons was reported in its previous report.

An adverse event for vaccination is any undesirable medical condition that occurs after taking the vaccine, which does not necessarily have a direct link to the treatment. They may be coincidental or related to an undiagnosed disease. These have to be reported by healthcare providers to HSA.

The authority said that most of the adverse events reports that it has received “are largely expected with vaccination and reflect what has been reported in the clinical trial”.

“Based on HSA’s assessment, the benefits of the Pfizer-BioNTech and Moderna Covid-19 vaccines continue to outweigh the known risks in a pandemic.             

“HSA and the Ministry of Health will continue to monitor the safety profile of the Covid-19 vaccines closely and update members of the public of any significant safety concerns detected with the vaccines,” it said.