3rd dose may be needed 18 months from last COVID vaccine jab: MOH official

SINGAPORE —While health authorities here expect the Pfizer-BioNTech and Moderna vaccines to confer protection against the coronavirus for up to 18 months, a booster dose may eventually be needed in vaccinated individuals in order to guard against new variants of COVID-19.

"While vaccination gives a clear protective benefit to all who may be exposed to COVID-19 infection, the vaccination is not 100 per cent protective. (And) beyond (18 months), it's still a relatively uncertain situation," said director of medical services Kenneth Mak at a virtual news conference on Thursday (22 April).

He added that the possibility of a booster dose, in addition to the two vaccine doses administered to individuals, has been studied by Singapore as well as other countries.

Associate Professor Mak pointed to two developments that may determine the need for a third dose. Firstly, "gradually waning immune protection" that may occur in vaccinated individuals, which has been seen in those who were re-infected with COVID-19.

And secondly, viral variants of concern, such as the UK, Indian and South African variant that have emerged worldwide in recent months, and which may be resistant to vaccines currently in use. A total of 350 local and imported cases of various COVID-19 variants have been detected in Singapore as of Tuesday.

"And if that were the case, it may well be the case that we need booster vaccine doses to augment the immunity that we already have from the previous vaccinations and to give us additional protection, particularly against these variants of concern."

Second Minister for Manpower Tan See Leng said at the conference that the authorities are looking to give a single booster shot to workers who have recovered from COVID-19.

“Studies have shown that there is a boosting of the immunity after you’ve given them a single shot, so we do have plans for that,” he said.

The Pfizer-BioNTech and Moderna COVID-19 vaccines are the only two authorised for use here.

Preliminary studies show that the vaccines from AstraZeneca and China's Sinovac are partly effective against the Brazilian variant. The Pfizer-BioNTech vaccine, one of two approved for use here, has also proven effective against the strain, but studies show it is less effective against the South African variant.

Two new Moderna vaccines designed to protect against the South African and Brazilian variants have yielded promising results when tested in mice, according to recent data. The original Moderna vaccine is approved for use in Singapore.

As of last Sunday, some 1.36 million individuals in Singapore have received at least one dose of either the Pfizer-BioNTech or Moderna vaccine, with more than 849,700 of them having received their second dose of the same vaccine and completed the full vaccination regimen.

A breakdown of how many of each vaccine type is administered here is not publicly available.

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