2 doses of Pfizer-BioNTech vaccine plus Moderna booster jab has ‘slight edge’ in reducing Covid-19 risk: MOH study

• A study was done to compare the effectiveness of Pfizer-BioNTech and Moderna vaccines as booster shots
• It found that people who took two doses of the Pfizer-BioNTech vaccine followed by a Moderna booster shot had a 'slight edge' in reducing the risk of getting Covid-19 
• This combination further reduces the risk of infection by 72 per cent, compared with 62 per cent if all three doses were Pfizer-BioNTech
• MOH's vaccine trial for children is making progress and the recruitment of the first group of participants will start soon
• Six children have so far suffered from multi-system inflammatory syndrome linked to Covid-19 as of Nov 15

SINGAPORE — A study by the Ministry of Health (MOH) on Covid-19 booster shots has found that two doses of the Pfizer-BioNTech vaccine followed by a Moderna booster shot has a “slight edge” in terms of reducing risk of infection, when compared with taking three doses of Pfizer-BioNTech.

Speaking during a media conference by the ministerial task force on Covid-19 on Monday (Nov 15), Health Minister Ong Ye Kung said that some members of the public had asked MOH about which booster vaccine to choose.

MOH thus conducted a study recently on the relative effectiveness of Pfizer-BioNTech and Moderna as booster vaccines in terms of reducing infection, he said.

The study compared two combinations: The Pfizer-BioNTech vaccine for all three doses versus two initial shots of the Pfizer-BioNTech vaccine and Moderna as the third dose.

He added that there are also results for other combinations, such as all three shots of the Moderna vaccine and two shots of Moderna with a Pfizer-BioNTech booster, but cautioned that “sample sizes for these are not very large and the statistics may not be as meaningful”.

“Relative to two Pfizer-BioNTech doses, three doses of the Pfizer-BioNTech vaccine further reduces risk of infection by 62 per cent. As for the two doses of Pfizer-BioNTech vaccine followed by a Moderna booster, the reduction is 72 per cent. So both mRNA vaccines work very well as boosters, with (the seond combination) having a slight edge,” he said of the findings.

“Regardless, the impact on the reduction of severity of illness is extremely high for both combinations.”

The Pfizer-BioNTech and Moderna vaccines are vaccines that uses a new messenger ribonucleic acid (mRNA) technology and are approved under the national vaccination progremme here.

Mr Ong also noted that the expert committee on Covid-19 vaccination advising the Government has recommended that the two mRNA vaccines can be used interchangeably, regardless of whether the first two doses were Pfizer-BioNTech or Moderna.

Mr Ong has also been receiving queries on why Singapore’s vaccination rate of 85 per cent is lower than that of other countries, he added.

This is because some countries report the vaccination rate as a percentage of the vaccine-eligible population, while Singapore reports it as a percentage of the total population.

“So if we break it down, 85 per cent of our population is fully vaccinated, so there's a remaining 15 per cent. And if we break down the remaining 15 per cent who are not vaccinated, it comprises as follows: 1 per cent who are not living in Singapore, 9 per cent who are children below 12 and not eligible, and the remaining 5 per cent who are eligible but chose not to vaccinate,” he explained.

“And so, if we recalculate this based on eligible population, we are around 94 per cent vaccinated. It is one of the highest coverages in the world.”

MOH will provide both figures in its daily press release on the Covid-19 situation to give a fuller picture of the progress of Singapore’s vaccination exercise, he added.

The ministry's vaccine trial for children, which it announced earlier, is also making progress, with KK Women's and Children's Hospital overseeing and planning to start recruitment of the first group of participants, Mr Ong revealed.

“The purpose of this trial is to smoothen operations when we have to do it at scale because young children are involved.”

The expert committee on Covid-19 vaccination is assessing whether to immunise children aged five to 11 years in Singapore with the Pfizer-BioNTech vaccine, after the United States approved the use of this vaccine for children in that age bracket.

The committee is expected to make its recommendation in the second half of this month.

In the meantime, MOH has signed a new supply agreement with Pfizer-BioNTech, which includes the delivery of paediatric vaccines, and it is in constant contact with the biopharmaceutical firm, which will try to fulfil the deliveries as soon as possible.

Also speaking at the media conference, MOH’s director of medical services Kenneth Mak said that there have been six cases of multi-system inflammatory syndrome in children (MIS-C) linked to Covid-19 as of Monday. They range in age from two months to 11 years old. 

It is a rare syndrome linked to a previous infection of the coronavirus and is known to cause symptoms such as persistent fever and difficulty in breathing.

Three of the children have made a good recovery and have been discharged home, he said, adding that they do have follow-up checks with specialists.

Of the remaining three, one had been admitted at first to a paediatric intensive care unit, but had responded well to treatment. He has since been transferred to a general ward and may be discharged soon if he continues to recover uneventfully, Assoc Prof Mak said.

Another child is being monitored in a high-dependency ward and is being treated for other concurrent infections. 

The last child is stable and is in a general ward.