SINGAPORE - Local transmission of Covid-19 in the general community has been low, at least up until the middle of March, researchers from the Covid-19 research group at the National Centre for Infectious Diseases (NCID) have found.

This shows that Singapore's contact tracing efforts have been effective, according to three studies by the NCID that are among the first of their kind in the world.

However, this also means that immunity rates here are low and much of Singapore's population remains susceptible to the virus, NCID executive director Leo Yee Sin told reporters on Wednesday (April 29).

For their seroepidemiology studies, researchers harnessed locally developed tests which detect antibodies produced in response to an infection and remain in a patient's blood after recovery.

This can help identify patients who were previously infected with a virus.

The three studies aimed to determine the proportion of the Singapore population infected by the virus and to understand how key populations such as front-line healthcare workers have been affected.

They were conducted between February and April, and reflect case figures before numbers began to spike in early April.

One study involving the general community tested 268 children aged 16 and below, as well as 506 adults of all ages.

Another of the studies involved 1,096 healthcare staff at the National University Hospital, Tan Tock Seng Hospital and NCID. About half of the staff were caring for Covid-19 patients or worked in areas with some risk of exposure to the virus.

Both of these studies found no clear evidence of past infection among the samples.

Dr Mark Chen, who heads the NCID's research office, said this showed that a "very low" proportion of the general community in Singapore were infected as of mid-March, and that local protections for healthcare workers have been adequate.