Around half of the Covid-19 cases in the cluster at 115 Bukit Merah View Market and Hawker Centre - Singapore's largest open cluster with 82 infections as at Wednesday night - were not vaccinated.
At least 219,000 tests have been conducted in various nearby areas over the past three weeks as part of aggressive community surveillance measures.
And among Singapore's community clusters, common settings where the virus is spread include the workplace and office, food and beverage outlets, as well as households.
Singapore's director of medical services Kenneth Mak gave these updates during a multi-ministry task force press conference yesterday afternoon.
He revealed that the first case in the 115 Bukit Merah View cluster was a sundry store owner. The virus then spread to other stall owners, tenants, social contacts and patrons of the market and food centre.
In this cluster, 36.7 per cent of them are fully vaccinated. More than half - 46 - of the total cases were not household-related; 16 were detected through surveillance or community testing operations; and 27 were isolated or quarantined before detection, said Associate Professor Mak.
The market and hawker centre will remain closed until tomorrow.
Prof Mak also noted the presence of other clusters in the vicinity, such as in Tiong Bahru, Redhill and the Enabling Village, a community and social enterprise hub nearby.
The Ministry of Health is tracking and studying these clusters to confirm if there are links to the 115 Bukit Merah View cluster.
There were 39 community clusters as at Wednesday night.
Three of the 10 large clusters will close by the end of this month if there are no more cases detected within them, said Prof Mak. These include the clusters at 506 Hougang Avenue 8 and Chevy's Bar and Bistro.
He noted that while overall community numbers have increased in the past week compared with the week before, the proportion of unlinked cases has dropped from 25 per cent to 21 per cent over the same period.
Of the linked cases, 46 per cent were already in quarantine and 33 per cent were detected through surveillance. The share of infections picked up on entry into quarantine has also decreased, from 18.8 per cent on June 16 to 5.5 per cent on June 22.
"This suggests that we are getting more cases more quickly, as a result of the aggressive testing that we've been doing," said Prof Mak.
He added that all five cases in intensive care as reported on Wednesday were unvaccinated.
"It reinforces our concern that those who are not vaccinated, if infected, may get a more severe case of the disease, may require oxygen supplementation, or even ICU care," he said.
He repeated the call for those who have yet to be vaccinated to register for their jabs.
"Our seniors, in particular, will be hard hit if the clusters increase, or if more clusters like what we see in Bukit Merah break through in our community," said Prof Mak.