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2.2m Covid-19 vaccine doses given; 95 ‘serious adverse events’ reported: HSA

SINGAPORE — Around 2,800 “adverse events” have been reported out of the 2.2 million vaccine doses administered here between December last year and mid-April, the Health and Sciences Authority (HSA) said. They are side effects that include rashes, fever and muscle aches. Of these, 95 were serious adverse events.

2.2m Covid-19 vaccine doses given; 95 ‘serious adverse events’ reported: HSA

A man receives his vaccination at a Covid-19 vaccination centre in Singapore on March 8, 2021.

  • There were 2.2 million vaccine doses administered here between December 2020 and mid-April 2021
  • So far, there were 95 reports of serious adverse effects on people vaccinated
  • HSA said the incidence of anaphylaxis is higher than for other vaccines, it still falls within expectation
  • On heart attacks and strokes, the authorities have not detected any safety concerns from the vaccines used


SINGAPORE — Around 2,800 “adverse events” have been reported out of the 2.2 million vaccine doses administered here between December last year and mid-April, the Health Sciences Authority (HSA) said. They are side effects that include rashes, fever and muscle aches. Of these, 95 were serious adverse events.

Stressing that there are no indications of strokes or heart attacks linked to the two vaccines used in Singapore so far, HSA said on Thursday (May 6) that the number of severe adverse events comprise only 0.004 per cent of the total doses given out in that period.

Most people who suffered these events have recovered or are recovering.

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

No deaths have been linked to the jabs, HSA emphasised in its first monthly safety update on the vaccines. The two vaccines being used in Singapore are Moderna and Pfizer-BioNTech.

Giving a further breakdown, HSA said that there were a total of 20 anaphylactic events, which is a rare and potentially life threatening allergic condition that the authority highlighted as an “adverse event of special interest”. Another 20 cases of severe allergic reactions were reported.

This works out to 1.4 cases of anaphylaxis for every 100,000 doses of the Covid-19 vaccine, which is higher than the rate of such incidents for most vaccines, the authority’s spokesperson said at a media briefing on Thursday.

However, this figure is similar to the incidence rates for Moderna and Pfizer-BioNTech vaccines that were reported overseas. 

HSA said that 80 per cent of those who suffered from anaphylaxis were women, 55 per cent of whom had a history of allergies to drugs or food.

The onset of symptoms for 60 per cent of these anaphylaxis cases came within the 30-minute observation period after the vaccine is given.

Another 25 cases of Bell’s Palsy were detected after the vaccines were given, though this is still within the incidence rate before vaccination. This indicated that the vaccine might not be linked to the reaction.

Bell’s Palsy causes temporary weakness or paralysis of facial muscles and patients often recover completely from this without the need for treatment. Both anaphylaxis and Bell’s Palsy have been categorised as adverse events of special interest, HSA said.

In terms of demographics, people under 60 were more likely to report adverse events from both vaccines as opposed to older people, the data showed. Around 70 per cent of the reports of adverse events came from this younger group.

HSA said that more than four in 1,000 persons between 20 and 39 reported adverse conditions such as rashes, hives, dizziness and fever, compared with the 1.2 in 1,000 persons between 60 and 69 years old who reported the same reactions.

Explaining why, HSA said that it is natural for younger people to experience more adverse events to the vaccines due to their more active immune response, which is part of the body’s response to an infection.

These reactions were in line with what the authorities know about adverse events that can arise from the two vaccines given special approval for use in Singapore.

Professor Teo Yik Ying, dean of the Saw Swee Hock School of Public Health who was also present at the briefing, said that anaphylaxis remains one of the greatest concerns in relation to the vaccines because it is potentially fatal if there is no early intervention.

“The good news is that the majority of the anaphylactic events do happen within a very short time after getting the vaccine, and that is why we have that 30-minute observation period (after people get the jab), which helps identify people who are experiencing anaphylactic shock.” 

Based on available data, the benefits of the Pfizer-BioNTech and Moderna vaccines continue to outweigh the known risks in a pandemic, HSA said.


HSA is also monitoring other severe adverse events such as the cases of unusual blood clots following the use of the Oxford-AstraZeneca and the Johnson & Johnson vaccines overseas, as well as reports of severe medical events such as stroke and heart attacks.

Neither of these vaccines is being used in Singapore.

No cases of blood clots have been reported with both the Pfizer and Moderna vaccines so far, HSA said.

On the instances of strokes and heart attacks that have occurred here, HSA said that there is “no signal” of safety concerns from the vaccine based on data from countries where larger populations have been vaccinated.

In February, a 72-year-old man with a history of cancer and hypertension was hospitalised for cardiac arrest following his first jab of the Pfizer vaccine. Last month, a 48-year-old man reportedly suffered from three strokes after getting his vaccination.

The authorities also sought to correct falsehoods in April of “clear and causal” links between strokes and heart attacks and the vaccines. The falsehoods included claims over an 81-year-old man who died from an ischaemic heart disease following vaccination.

Elsewhere, Israel has been investigating a small number of cases of heart inflammation, or myocarditis, in people who received the Pfizer vaccine. The manufacturer had said that it has not observed a higher incidence of this condition than would be expected normally.

When asked about this, an HSA spokesperson said that strokes and heart attacks occur naturally in people for various reasons, such as underlying chronic conditions. They are more likely to occur among those who are older and can also happen spontaneously, she added.

The authority is also monitoring these types of adverse reactions closely, grouping these cases to see if there are any “unusual patterns” and whether it can find any causal link to vaccines.

“A greater frequency of heart attacks and strokes has not been observed in vaccinated persons locally and to date, there is also no evidence that the vaccines can directly cause these events,” HSA said in a statement.

A Ministry of Health (MOH) spokesperson said that clinicians will take all signs and medical histories of stroke and heart attack patients in totality to determine if they are related to vaccines.

MOH had also commissioned the Saw Swee Hock School of Public Health to conduct a study to see whether the numbers of stroke or heart attacks of vaccinated persons were within the baseline incidence rates, he added.

Presenting the findings, Prof Teo said that around six people in Singapore will experience a heart attack within a 24-hour period, with or without vaccination. So far, there has been no “overrepresentation” of these major medical events among vaccinated persons, he said.

Around 20 per cent of Singapore’s population has been vaccinated, Prof Teo added. A total of 92 per cent of the vaccinated persons in Singapore received the Pfizer vaccine.

“That is where the numbers help to provide some reassurance, in terms of whether we are seeing an overrepresentation of major medical events (compared with those that occur) by chance,” he said.

He added that besides looking at numbers, the authorities also look into whether there are any clinical and “mechanistic” links between vaccines and these medical events.

Urging people to continue to be vaccinated, Prof Teo said the statistics show that adverse events from vaccines are within the range of what has been reported overseas.

Prof Teo then noted that the recent cases of community infections, including the Tan Tock Seng Hospital cluster, also show that vaccinations help reduce the severity of the illness caused by Covid-19.

He said: “We know that vaccines provide much better protection against the serious outcomes of infection. So, vaccination with Pfizer and with Moderna… continue to be effective, not just locally but overseas as well.”

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Covid-19 coronavirus vaccine HSA Pfizer-Biotech Moderna

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