"It's the same reason that age group was selected early for vaccines, the same reason that age group has been selected for booster jabs."
Singapore has been a model for coronavirus mitigation since the pandemic began with mandatory masks, effective contact tracing and a closed border.
In all, 62 of its 5.7 million people have died and new daily infections were for months no more than a handful.
But, as elsewhere in Southeast Asia, the Delta variant has in recent months been spreading and new daily cases have risen to about 1,000.
Several countries including the United States, France and Italy have announced mandatory vaccination programmes, concerned the Delta variant and a slowdown in vaccinations will thwart plans to get back to normal.
Of vaccinated people in Singapore who caught the virus from May 1 to Sept. 16, only 0.09% of them had to go into intensive care or died. The rate for the unvaccinated was 1.7%.
Data for the elderly is particularly striking.
Of infected unvaccinated people aged 80 or older, 15% of them had to be treated in intensive care or died. Only 1.79% of the vaccinated in that age group needed intensive care or died.
Singapore has not made vaccination compulsory because the Pfizer and Moderna shots only have emergency approval in the country although it has limited activities such as eating out for the unvaccinated.
Neither company responded to a query on whether it had applied for full approval in Singapore.
With about 87,000 seniors still unvaccinated, some experts say full approval could pave the way for a mandate.
"Vaccination is much more protective than the other measures we have in place, and less economically and socially damaging," said Alex Cook, an infectious disease modelling expert at the National University of Singapore.
"If we are not to enforce vaccination, it seems odd to enforce weaker and more costly measures."
The number of patients requiring oxygen support or intensive care jumped more than five-fold this month to 146, including 18 in ICU.
The government is worried the numbers in ICU could grow quickly on an exponentially rising base of infected people, especially if they are elderly and unvaccinated.
Singapore has about 100 ICU beds for COVID-19 patients, and it can increase that to nearly 300 at short notice.
A vaccine mandate could take the form of curtailing activities for unvaccinated people related to their work, leisure and use of public transport, said infectious diseases doctor Leong Hoe Nam.
"You cannot go to the malls or take public transport or eat out unless vaccinated," he said, giving examples of possible restrictions.
Only vaccinations against diphtheria and measles are mandated by law in Singapore.
The government has been offering the Pfizer and Moderna vaccines for free and it has also approved payouts to 144 people who suffered serious side effects, media reported.
Singapore has a long record of imposing rules, including a famous 1992 ban on the sale of chewing gum to prevent littering, but nevertheless compulsory vaccines would be a significant step.
"It will take political courage, there's no doubt about that, but the science would say you will save hundreds of lives if you vaccinate the last 100,000 seniors," said Fisher.
(Reporting by Aradhana Aravindan in Singapore; Editing by Miyoung Kim, Robert Birsel) ((email@example.com;))