SINGAPORE - To vaccinate as many people against Covid-19 as soon as possible, Singapore has decided to delay the second vaccine dose by two to five weeks.
This means that the interval between the first and second jabs will be extended to six to eight weeks, from the current three or four weeks.
This will allow 400,000 more people to get at least one dose without materially impacting the eventual overall immune response, as long as the second dose is eventually administered, said Health Minister Ong Ye Kung on Tuesday (May 18).
When the Health Sciences Authority approved the mRNA vaccines for use here, they could already be given six weeks apart. Singapore's expert committee on Covid-19 stated in a press release on Tuesday: "This is based on the maximum dosing interval that was adopted during the pivotal trials."
Several countries including Britain and Germany have also been widening the interval between doses. Some give the second dose as long as 12 weeks after the first, to get as many people vaccinated as quickly as possible, in the face of a shortage of vaccines.
The first dose of the mRNA vaccines used here gives about 75 per cent protection 12 days after it is given. This goes up to about 95 per cent protection with the second dose.
Referring to a study done in Britain, the committee said "based on early evidence in persons aged above 80, such a delay of the second dose to 12 weeks resulted in higher antibody levels two weeks after the second dose".
Asked how the decision was reached to extend the interval between vaccine doses to six to eight weeks, Singapore's director of medical services, Associate Professor Kenneth Mak, said there are still some issues to be resolved about having a longer interval.
"Across different jurisdictions, different countries, we seem to be coming to some form of agreement independently that it is acceptable to lengthen the dosing interval," Prof Mak said.
"But it would probably be somewhere around the region of six to eight weeks, which would be reasonable for us to anchor on at the onset."
The expert committee said that "given the nascent data... a cautious extension of the interval between the first and second dose to six weeks is unlikely to be an issue". It also indicated concern if the delay were beyond eight weeks.
Singapore's vaccine roll-out is constrained by the delivery schedule. While Singapore has bought enough vaccines for everyone, how fast they can get into arms will depend on how fast the vaccines arrive.
Mr Ong said extending the interval between jabs will give "priority to first dose so that we cover as big a proportion of our population as possible".
With the longer interval between doses, another 300,000 people can get their first dose this month, with 4.7 million, or almost all eligible people, getting at least one vaccine dose by August.
Said Mr Ong: "Altogether, we will be able to reach 4.3 million vaccinated individuals by the end of July. Status quo, we would have reached 3.9 million.
"But with this new strategy of prioritising first dose, we will reach 4.3 million, so 400,000 more individuals will be vaccinated."
So far, 1.4 million people here have received both doses and another 600,000 have had one dose. These 600,000 people may continue to get their second dose as scheduled.
But Mr Ong urged: "Amongst those who have booked but (are willing to) volunteer to push back your second dose appointment so that that dose can be given to someone else for their first dose, please do so.
"You can call our vaccination call centre at 1800-333-9999. So you can do that and you will do another Singaporean a favour."