​A COVID-19 treatment authorised here in 2021 is no longer recommended for use, said the National Centre for Infectious Diseases.

NCID clinical director Shawn Vasoo said the centre does not recommend the use of casirivimabimdevimab – used to treat mild to moderate COVID-19 cases – because of its poor activity against Omicron variants.

The Health Sciences Authority granted casirivimab-imdevimab interim authorisation under the Pandemic Special Access Route in September 2021.

About two weeks ago, the World Health Organisation (WHO) said it strongly advised against using casirivimab-imdevimab and sotrovimab, another COVID-19 treatment, because they were less effective against newer variants.

The two antibody treatments work by binding to the spike protein of the SARS-CoV-2 virus, limiting its ability to infect cells.

The United States Food and Drug Administration said in April that it no longer authorises the use of sotrovimab to treat COVID-19.

While sotrovimab retains some activity against Omicron variants BA.1 and BA.1.1, it has poorer invitro neutralisation against the BA.2, BA.4 and BA.5 variants, Dr Vasoo said. He added that the national COVID-19 Therapeutic Workgroup, which he leads, has since April 28 advised that a higher dose of sotrovimab be used if the drug’s use is being considered.

One other antibody treatment, tixagevimab-cilgavimab, is available in Singapore and retains at least some activity against the BA.2, BA.4 and BA.5 Omicron variants, he said, adding that it is more effective than sotrovimab.

Dr Vasoo noted that the predominant circulating variants are now BA.4 and BA.5, and that the SARS-CoV-2 virus continues to evolve.

Given the limitations of antibody drugs in treating COVID-19, alternative treatments should be considered, he said. These include antiviral drugs such as Pfizer’s Paxlovid or MSD’s Lagevrio, which were approved here earlier this year.

“There remain some sub-groups of patients, though, who may benefit from antibody treatment, and the COVID-19 Therapeutic Workgroup will be reviewing its recommendations with the evolving data and also WHO’s recent guidance.”

The Ministry of Health on Friday said there has been a 35 per cent to 40 per cent week-on-week rise in daily COVID-19 cases in the past few days due to an increase in BA.2.75 variant cases, accounting for about a quarter of all daily infections.

But this has not led to more severe cases, and there has been no significant impact on the healthcare system.

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