Will Covid-19 drugs be less effective against Omicron variant?

As the highly mutated Omicron coronavirus variant surfaces in more places around the world, there is concern that it will evade a class of drugs - known as monoclonal antibodies - that can help prevent a person from becoming very ill with Covid-19.

These monoclonal antibodies - laboratory-made versions of the antibodies produced by the body to fight Covid-19 - are designed to look for the spike protein of the coronavirus.

Associate Professor Luo Dahai from Nanyang Technological University's Lee Kong Chian School of Medicine said the mutations found in Omicron are mainly focused on the virus surface's spike proteins, which may thus make the spike protein-targeting antibodies less effective.

At Alexandra Hospital, Dr Louisa Sun, an infectious diseases consultant, said the main concern where drugs are concerned is monoclonal antibodies, as most other Covid-19 treatments do not target the virus.

Still, doctors and public health experts are watching closely to see whether Omicron will affect vaccine effectiveness and cause more severe disease and deaths, she said.

Currently, the commonly used drugs for Covid-19 fall under three main categories - antibody treatments, anti-inflammatory drugs and antivirals.

Antibody treatments can block the coronavirus from entering human cells and neutralise it. Monoclonal antibodies are given to patients early in the course of illness.

"These are injectable drugs and are costly as their production process is complex," said Dr Sun.

Patients need to be carefully screened for their suitability to receive monoclonal antibodies, because "if given too late or to unsuitable patients, they have no benefit", she said, and may cause harm instead. Omicron's impact: Antibody treatments may be less potent as these target the spike protein of the coronavirus. Regeneron has said its antibody cocktail may be less effective against Omicron, while GlaxoSmithKline said laboratory tests showed that its antibody drug works against the new variant.

Anti-inflammatory drugs are used to calm the immune system's violent reactions to the virus in the sickest patients.

The most important and commonly used drugs for Covid-19 patients who need oxygen or are in the intensive care unit are steroids, said Dr Sun.

But they are not recommended for mildly ill patients who do not need oxygen, she added.

Dexamethasone was the first steroid found to be effective in reducing deaths from Covid-19. Apart from steroids, there are a few other drugs used to suppress inflammation, and they are known collectively as immunomodulators.

When deciding which drugs are suitable, doctors will also need to consider the patient's underlying conditions and other complications, said Dr Sun. Omicron's impact: "Drugs that target the immune system, such as tocilizumab or dexamethasone, do not target the virus at all and therefore are unaffected by viral mutation," said Associate Professor Hsu Li Yang, an infectious diseases expert at the National University of Singapore Saw Swee Hock School of Public Health.

Antiviral drugs prevent the coronavirus from multiplying inside the body.

There is remdesivir, which can be added to steroids to treat very ill patients. It is a lot more costly than steroids.

There are also the newer oral antivirals, such as molnupiravir from Merck and paxlovid from Pfizer.

Dr Sun said these drugs, similar to monoclonal antibodies, are given early to patients when they still have mild disease. "However, there are still several unknowns at this point as well, and due to various side effects, there will still be sub-groups of patients who will not be able to receive these treatments," she added.

Singapore has signed an agreement to buy molnupiravir, and said in October that the antiviral pill will be available once it is approved by the Health Sciences Authority.

But will members of the public be able to go to the general practitioner soon to get a pill when they become sick with Covid-19? Prof Hsu said this will not be likely soon, because professional bodies have to be satisfied that the drugs can be prescribed by family practitioners and the price has to be low enough such that GPs and patients will want to pay for it.

These drugs are not cheap. Prof Luo said: "Most of the new drugs are expensive as the pharmaceutical companies want to make a profit, from hundreds to thousands of dollars."

At the National Centre for Infectious Diseases, clinical director Shawn Vasoo said the centre is anticipating further data for the newer oral antivirals.

He added that the antivirals could benefit those who are at higher risk - the patients currently being cared for at Covid-19 treatment facilities or in hospital. Omicron's impact: Drugs that specifically target the virus, such as Gilead's remdesivir, Merck's molnupravir and Pfizer's paxlovid, zero in on parts of the virus that still remain conserved in current Covid-19 variants, said Prof Hsu.

Prof Luo said that while more research is needed to confirm that Omicron will not reduce the efficacy of antivirals, these drugs target the viral replicative proteins "which seem not to carry any critical mutations".