Moderna more effective as a booster shot for those over 60 who received Pfizer vaccination

A booster shot with the Moderna vaccine offered older people better protection against Covid-19 if they had previously taken the Pfizer jabs, researchers at the National Centre for Infectious Diseases (NCID) have found.

Seven days after taking a booster shot, people above age 60 who took Moderna had an average antibody level which was twice as high as those who took the Pfizer-BioNTech/Comirnaty vaccine, the study showed.

This was consistent across all variants of concern of the Covid-19 virus, said NCID in a press release on Thursday (March 17).

It added that the observations complement studies from other international trials.

Head of the Singapore Infectious Disease Clinical Research Network in NCID Dr Barnaby Young said the aim of the study is to build local data on understanding immunity towards the disease through booster shots.

"The emergence of variants capable of evading protective immunity remains a concern and highlights the need for a long-term Covid-19 immunisation strategy," he added.

The study, conducted between Oct 12 and Dec 3 last year, involved 100 participants who had received the Pfizer shots as their primary series of Covid-19 vaccination.

Half of the participants were above 60 years old.

Researchers observed that even at 28 days after vaccination, average antibody levels in older people remained 1.5 times higher in those who took the Moderna booster.

However, in younger adults, antibody levels were similar between the two vaccines.

The study involved blood samples collected 28 days before the booster shot, on the day of the booster shot but before the injection, and seven days and 28 days after the shot.

For those older than age 60, researchers observed that neutralising antibody levels against the Omicron variant with a Moderna booster were at 84.3 per cent 28 days after the shot versus 72.8 per cent with a Pfizer-BioNTech/Comirnaty booster.

Neutralising antibodies are thought to play an important role in immunity against the coronavirus.

Dr Young said taking Moderna as a booster shot may offer better or longer protection for older adults.

He added that based on the results of the study taking any booster shot helps increase immunity against the Omicron variant, even though it has been found to be able to escape immunity among fully vaccinated people

He added: "The magnitude of the antibody boost is likely to offer significant protection against infection with this variant.

"Individuals at higher risk of severe Covid-19 such as older adults 60 years old and above are more likely to have low antibody levels six months after primary vaccination series, so it is important that this group receives a booster shot."

The interim findings were published in SSRN, a science research journal, on Thursday, and have yet to be peer-reviewed.

NCID said the research is part of on an ongoing study it is leading on different vaccine combinations and immunity.

In the booster-shot study, it found that vaccine reactions were common, but were mild and short-lived.

Common vaccine reactions were pain at the injection site within 72 hours of a booster shot, fatigue, followed by muscle pain.

It added that in the older age group, fever and weakness occurred more frequently in those that received Moderna as a booster dose, and that no participant had a serious side effect.

Researchers will continue to follow participants and collect blood samples six months and a year after their booster shots to monitor waning of antibody levels.

They will also study the effects of mixing the Covaxin vaccine into a vaccination regime.

NCID said it will include other vaccines in the future including Nuvaxovid, and could involve up to 600 participants over a range of ages and ethnicities to reflect Singapore's population.