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The Health Sciences Authority (HSA) has authorised the use of Pfizer-BioNTech's Comirnaty Covid-19 vaccine for children between the ages of six months and four years old on Sep. 28.

Three 3-microgram doses

Following Moderna's Spikevax, the Comirnaty vaccine is the second HSA-authorised vaccine for young children in Singapore to use.

HSA wrote in its Sep. 29 press release that the vaccination regimen for the primary series in this age group consists of three 3-microgram doses.

The first two doses will be administered three weeks apart.

This will be followed by a third dose, which will be administered at least eight weeks after the second dose.

HSA said the official vaccination recommendation on the use of the Comirnaty vaccine will be issued by the Expert Committee on Covid-19 Vaccination and the Ministry of Health when it is ready.

Results from evaluating data on efficacy

Based on Pfizer's Phase 2/3 clinical study, the immune response of children in this age group with a three-dose primary series was comparable to that in adults aged 16 to 25 years who received their two primary doses vaccine, which were higher at 30 micrograms.

This implies that three doses of the vaccine may provide a similar level of protection in young children as that of two doses in adults.

For children aged 5 to 11 years, data has shown that two doses of the Pfizer vaccine were around 40 per cent effective against the Omicron subvariants, and over 80 per cent effective in mitigating Covid-related hospitalisations.

This implies that the vaccine would similarly protect younger children aged six months through four years from severe Covid-19 outcomes and other potential complications.

However, preliminary data from a secondary analysis of Covid-19 cases estimated the vaccine's efficacy to be lower at around 73 per cent.

According to HSA, the evidence was limited and should be interpreted with caution.

Mild to moderate adverse reactions

HSA stated that there were no cases of serious adverse events such as myocarditis/pericarditis (inflammation of the heart muscle) reported during the clinical studies with Comirnaty.

The adverse reactions in young children were similar to those reported in adults and were mild to moderate.

Commonly reported reactions include injection site pain, fever, fatigue and headache.

HSA said these reactions are generally associated with vaccinations and are to be expected as it is the body's natural response to build immunity against Covid-19.

These reactions tend to resolve on their own within a few days.

HSA recommends for caregivers to monitor their young children for signs and symptoms of myocarditis such as chest pain, breathing difficulty, etc., as well as take precautions to minimise rigorous physical activity following vaccination.

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Top image by Mika Baumeister from Unsplash