A 23-year-old Indian national with a work permit who had received both doses of COVID-19 vaccine was the sole locally transmitted case among 20 infections confirmed on Sunday.

The Health Ministry has warned that an individual can get infected even after vaccination.

The Indian, who worked as a lashing specialist, was detected as COVID-19 positive through pooled rostered routine testing on April 7, according to a news report.

After his polled test results came positive on April 8, he was immediately isolated and an individual test was conducted on April 9.

When the second result too was positive, he was taken to the National Centre for Infectious Diseases.

''This case is a reminder that it is possible for vaccinated individuals to get infected. But the vaccine is effective in preventing symptomatic disease for a vast majority of those immunised,'' the health ministry was quoted as saying in a media report on Sunday night.

It noted that the worker's serology test had come back positive, likely due to the antibodies produced following vaccination.

The Indian man testing positive for COVID-19 was the first in a workers' dormitory since February 28. Such facilities housing foreign workers had the highest COVID-19 cases during the peak of the coronavirus spread last year.

The health ministry said further research is required to determine if vaccination will prevent onward transmission of the infection.

''That is why we cannot afford to let our guard down,'' it said. ''Our existing key enablers — safe management measures, testing, and contact tracing — continue to be necessary and effective in helping us to mitigate the spread and keep community transmission low.'' Epidemiological investigations are underway, while all identified close contacts of the Indian man have been isolated.

They will be tested at the start and end of their quarantine period to detect any asymptomatic cases.

''We will also conduct serological tests for the close contacts,'' the health ministry said.

Singapore has so far reported 60,653 COVID-19 infections. With 13 patients discharged on Sunday, the total number of recoveries reached 60,320.

As of now, 58 patients remain in hospitals and one is in intensive care while 230 are recuperating in community facilities.

Singapore has had 30 deaths from COVID-19 complications, while 15 who tested positive have died of other causes.