The highly transmissible strain of Covid-19 that surfaced in India has become more prominent among Singapore's growing number of unlinked cases, in a sign that hidden chains of transmission of the variant have existed for some time.
Of the 17 unlinked cases identified on Sunday, six patients whose ages range from 29 to 57 years old preliminarily tested positive for the strain known as B.1.617, according to updated Ministry of Health data published overnight. Among them is a driver who was tested for the virus after developing a runny nose, an auxiliary police officer who had body aches, and an unemployed Malaysian national who saw a doctor after experiencing fever and cough. Among them, two had gotten their first vaccine dose already.
There have also been cases tied to the variant detected in India in the infection clusters seen at the country's airport and a large public hospital.
All in, Singapore reported 38 new cases of Covid-19 infection in the community on Sunday, the highest number in more than a year. The spike in unlinked local cases -- which increased to 32 cases in the past week from six cases the week before -- comes as Singapore returns to the lockdown-like conditions it last imposed a year ago, banning dining-in and limiting gatherings to two people. While the outbreak is smaller than the one last year centered on migrant workers, it is being driven by new variants, which are causing fierce new waves and outpacing vaccination progress in many places around the world.
On Sunday, Singapore further announced it will stop most in-person school classes this week, with its education minister saying some of the variants appear to attack younger children.
Countries like the UK have said the strain could lead to a major surge in cases and is accelerating its vaccine rollout. Meanwhile, Singapore's inoculation pace has been limited by supplies. The city-state is now studying holding off the second vaccine shot so that more people can get at least the first dose.
"If supply is limited, then giving more people a single dose while waiting for more supplies is a good strategy because the protection from the mRNA vaccines after one dose is quite high, said Raina MacIntyre, a professor of biosecurity at the University of New South Wales in Sydney.
She co-authored a study last month looking at requirements for herd immunity in Australia's New South Wales, which has a population size comparable to Singapore's. If using a vaccine of 90% efficacy against all infections, it finds you need 66% of the population to be fully vaccinated. So far, Singapore has vaccinated 1.9 million people, or a third of the population, with the first dose. About 1.3 million have received both doses.
"All precautions must continue while the vaccination program continues," she said. MacIntyre said that if the Indian variant, that is more transmissible, is dominant, "achieving herd immunity will require higher vaccination rates - maybe 75-80% vaccinated."
Singapore's virus situation could be more dangerous than it was just before a similar lockdown last year, warned David Lye, an associate professor at the National Centre for Infectious Diseases, according to the Straits Times. The many cases with no linkage suggest that the spread to the community from the outbreak at Changi Airport may be "wide and far," he said, according to the paper.
Singapore has reacted aggressively to the flareup linked to the variant by barring visitors from India last month and extending quarantines at government-designated facilities to three weeks.
"New strains of the Covid-19 virus seem to have slightly different characteristics from the previous strains," Chan Chun Sing, the new education minister said at a briefing on Sunday announcing the new school measures. "But one of the things that we have seen seems to be -- at least from our numbers -- there are more children who seem to have contracted this virus, so of course that is an area of great concern."