Singapore HSA: Adverse events of Covid-19 mRNA vaccine booster jabs similar to those of first two doses

People waiting at an observation area after receiving their Covid-19 vaccines. ― TODAY pic
People waiting at an observation area after receiving their Covid-19 vaccines. ― TODAY pic

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SINGAPORE, Dec 21 — The adverse events from messenger ribonucleic acid (mRNA) vaccine boosters are similar to those from the first and second doses of the vaccines, with no observed increase in the frequency of adverse events, the Health Sciences Authority (HSA) said.

In its vaccine safety report released yesterday (December 20), HSA said that the adverse events from booster shots included rash, chest discomfort, palpitation, shortness of breath, fever, generalised weakness and dizziness, and the swelling of eyelids, face and lips.

There have been no reports of anaphylaxis (a life-threatening allergic reaction) so far from the booster jabs, but there have been four cases of myocarditis, or heart muscle inflammation.

This was HSA’s eighth safety update, which gives an overview of suspected adverse events reported by healthcare professionals since the national vaccination exercise for Covid-19 began in Singapore on December 30 last year to Nov 30 this year.

An adverse event in this context is any undesirable medical condition that occurs after vaccination and this does not necessarily mean that the vaccine caused it.

These have to be reported by healthcare providers to HSA.

Serious adverse events result in hospitalisations, a significant reduction in functioning level, a life-threatening illness, a birth defect or death.

The following are some key points from the latest report.

Common adverse events

To date, a total of 10,630,775 doses of the Pfizer-BioNTech and Moderna mRNA vaccines have been administered, of which 0.13 per cent resulted in suspected adverse events.

The most commonly reported ones were allergic reactions, dizziness, shortness of breath, chest discomfort, palpitations, fever and pain or swelling at the injection sites.

These usually resolve in a few days, HSA said.

Among the serious adverse events, the most frequent ones were anaphylaxis and other severe allergic reactions.

Close to 80 per cent of the adverse events were reported in those younger than 60 years old.

HSA attributed this trend to the more active immune responses of younger people.

Adverse events among teenagers

Since the vaccine programme was rolled out to students aged 12 and above this June, HSA has received a total of 1,105 adverse event reports for mRNA doses administered to those aged between 12 and 18.

This is 0.17 per cent of the total number of doses administered to this age group.

The commonly reported adverse events are rash, hives, angioedema (the swelling of the eyelids, face and lips), shortness of breath, palpitation, chest tightness and discomfort, fever, dizziness, light-headedness and syncope or fainting.

The authority noted that these side effects resolve within a few days and are in line with similar reports overseas.

Sinovac and Sinopharm

Out of the 260,911 doses of the Sinovac vaccine administered here so far, there have been 235 reports of adverse events, equivalent to 0.09 per cent of the doses administered.

The commonly reported ones were rash, hives, shortness of breath, chest discomfort, dizziness and the swelling of the eyelids, face and lips.

There were 18 serious adverse events reported, equivalent to 0.007 per cent of the administered doses.

There were eight reports of anaphylaxis and all occurred in people who had previous allergic reactions with the mRNA vaccines or had multiple drug allergies.

The remaining 10 serious reports include myocarditis, Bell’s palsy (temporary paralysis of facial muscles), blood clots, numbness, muscle spasm, vertigo with tinnitus (ringing of the ears) and serious allergic reactions.

Since the Sinopharm vaccine was made available here from Aug 30, there have been 26 suspected adverse event reports. This is 0.04 per cent of the 66,408 doses administered.

The non-serious adverse events included rash, shortness of breath, numbness, syncope, chest discomfort, tinnitus and the swelling of the eyelids, face and lips.

There were two serious adverse event reports of low platelet count and chest pain with visual disturbance.

Adverse events of special interest

This refers to a medically significant event that has been observed historically with other vaccines. Examples of such adverse events included anaphylaxis, Bell’s palsy, myocarditis and pericarditis (inflammation of the outer lining of the heart).

1. Anaphylaxis

The incidence rate of anaphylaxis reported here with the mRNA vaccines is about 0.94 per 100,000 doses administered, which is similar to the incidence rates reported overseas.

HSA said that it has not received any reports of anaphylaxis following booster doses so far.

It has recommended to the Ministry of Health that the observation time following booster shots of the mRNA vaccines may be reduced from 30 to 15 minutes.

2. Myocarditis and pericarditis

The authority has received 94 adverse event reports of myocarditis and pericarditis following more than 10.63 million doses of mRNA vaccines administered.

The overall incidence is estimated at 0.96 per 100,000 doses administered, with males aged 30 and below appearing to have the highest risk.

3. Bell’s palsy

To date, 117 cases of Bell’s palsy have been reported, with most of the reports being non-serious. There does not appear to be an increased risk of Bell’s palsy from vaccination, HSA said.

Most of the adverse events reported here are largely expected and reflect global reports.

It added that the benefits of the Pfizer-BioNTech, Moderna and Sinovac vaccines continue to outweigh the known risks of contracting Covid-19. ― TODAY

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