SINGAPORE – As the Covid-19 virus continues to evolve, the Ministry of Health (MOH) and Singapore’s Expert Committee on Immunisation (ECI) continue to recommend an additional dose in 2024 for those who are medically vulnerable.
They also encourage all who are aged six months and above to get vaccinated a year after their last dose.
This is in response to a recent study by the NUS Yong Loo Lin School of Medicine (NUS Medicine) and Duke-NUS Medical School, which said the immune response from two doses of mRNA vaccine is enough to protect children against Covid-19 and that a third dose is not needed as it does not extend the benefit.
In an e-mail to the media, MOH said it is aware of a recently published local study but it continues to stand behind the analysis of its own local data, comprising information from more than 250,000 children aged five to 11 years between September 2021 and August 2023.
It demonstrated that the protection against hospitalisation in local children increased from 66 per cent with two vaccine doses to 73 per cent with three vaccine doses.
It said there have been local and international studies looking at actual clinical outcomes that demonstrate enhanced protection against Covid-19 with a booster dose in children.
It also cited a study in the United States that observed that the protection against Covid-19 infection among five- to 11-year-olds during the Omicron variant period increased from 20 per cent with two vaccine doses to 55 per cent with three.
MOH and the ECI regularly monitor vaccine developments and study findings, and will review and update their Covid-19 vaccination recommendations as needed, the ministry said.
In the NUS Medicine and Duke-NUS study, conducted from Dec 20, 2021, to March 8, 2022, 110 healthy children aged five to 12 were enrolled.
All participants received two doses of 10 micrograms (mcg) of the Pfizer/BioNTech mRNA Covid-19 vaccine, 21 days apart. For one year, the participants periodically donated blood to test for immune response to the vaccine.
A proportion of the children received a booster dose five months after completing two doses.
All participants took antigen rapid tests using home kits when Covid-19 infection was suspected. This was reported to the study team when the results, positive and negative, were confirmed.
The study found that while antibodies waned with time and their protective capacity decreased in the face of different forms of the virus, other parts of the immune system, such as the T-cells and memory B cells, provided lasting protection against symptomatic Covid-19 infection.
This means that enough T-cells and memory B cells were generated after two doses of mRNA vaccine, and that their levels were not improved with a third, or booster, dose.
T-cells help protect the body from infection, and memory B cells remember particular infections, allowing the immune system to mount a defence quickly.
The paper was published in Nature Medicine on April 30, 2024.
