Covid-19 antibody treatment no longer recommended as it is not effective against Omicron variants

NCID does not recommend the use of casirivimab-imdevimab due to its poor activity against Omicron variants. ST PHOTO: KUA CHEE SIONG

SINGAPORE - A Covid-19 treatment which was authorised here last year is no longer recommended for use, the National Centre for Infectious Diseases (NCID) said.

NCID clinical director Shawn Vasoo said the centre does not recommend the use of casirivimab-imdevimab - used to treat mild to moderate Covid-19 cases - due to its poor activity against Omicron variants.

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

On Sept 15, 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 in-vitro neutralisation against the BA.2, BA.4 and BA.5 variants, Dr Vasoo told The Straits Times.

He added that the national Covid-19 therapeutic work group, 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 efficacy against the BA.2, BA.4 and BA.5 Omicron variants, he said, adding it is more effective than sotrovimab.

Dr Vasoo noted 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.

They 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 work group will be reviewing its recommendations with the evolving data and also WHO's recent guidance," he said.

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

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

MOH reported 3,431 Covid-19 cases here on Thursday.

There were 247 patients hospitalised, with nine in intensive care and 15 requiring oxygen support.

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