AstraZeneca’s Evusheld

Australia’s drugs regulator, the Therapeutic Goods Administration (TGA), has granted “provisional determination” to pharmaceutical company AstraZeneca for a long-acting antibody cocktail which has shown promise in preventing Covid-19 in adults.

What is the treatment?

This treatment consists of two laboratory-made antibodies, tixagevimab and cilgavimab. These antibodies bind to the spike protein of the virus, stopping the virus from entering the body’s cells and causing an infection.

How does it work?

AstraZeneca’s Evusheld is not a vaccine but a treatment with two antibodies that target and neutralise coronavirus. It provides antibodies directly to the body via two intra-muscular injections administered consecutively. It immediately targets and neutralises the virus, preventing the virus from entering cells and causing an infection in the first place. 

Who will benefit from it?

If approved, Evusheld will be the first long-acting antibody available for Covid-19 prevention in vulnerable populations who are unable to mount an adequate immune response to the virus from vaccination alone, for example people with cancer, and some elderly people.

When to roll it out to the general population?

Evusheld also takes longer to administer, is more expensive, needs to be given by a trained doctor or nurse, and patients may need longer monitoring afterwards than the 15 minutes required for a vaccine. It is not something that can be quickly given in a pharmacy or hub, so it is not ideal for widespread, fast rollout, Hamad said. Plus, further data from ongoing trials is still needed, while the efficacy and safety of the vaccines are now well known.

Pfizer’s Paxlovid

Pfizer says its antiviral COVID treatment Paxlovid cuts the chance of ending up in hospital or dying by 89 per cent. The phase 2/3 trial data on which those hospitalisation rates are based have yet to be independently verified. Nor has the treatment been approved by any country for use outside a clinical trial.

What is the treatment?

Paxlovid is a combination of two different drugs – the HIV drug ritonavir (a capsule) and an experimental drug PF-07321332 (a pill).

How does it work?

Paxlovid is one potential COVID drug for use at home. The idea is these could be prescribed at the first sign of infection to prevent serious illness and death. People would manage their own symptoms, monitored while at home, and only be transferred to hospital if their condition deteriorates.

Who will benefit from it?

If patients with mild COVID have certain risk factors for disease progression, such as diabetes or a heart condition, doctors may consider using hospital administered treatments such as sotrovimab, Ronapreve, or inhaled budesonide to prevent disease progression.

According to Pfizer’s trial results, Paxlovid could be used as an alternative to in-hospital treatment for preventing disease progression in patients with the same risk factors.

When to roll it out to the general population?

Before the drug could be used in Australia, the Therapeutic Goods Administration (TGA) would need to assess its efficacy and safety. Just as importantly, the TGA would need to decide who may prescribe it and under what conditions. This may include whether it would be available from GPs, and what sort of patient risk factors would be considered.

Where next?

There are several steps before we can routinely expect to take COVID drugs at home to prevent the worst of the symptoms. We need independent verification of these drugs’ efficacy and safety, and of course, regulatory approval.

Then there’s the issue of cost.

Developing new medicines, particularly at the pace required because of COVID, means these new drugs aren’t cheap. One consideration for state and federal governments will be balancing the costs of the medicines against health outcomes.

The daily cost of a patient in hospital is around $5,000 for an uncomplicated (non-COVID) admission. This is much more than the reported cost of a full course of molnupiravir to the US government at US$700 (about $960).

But the costs of Paxlovid, and other new COVID medicines, have not been released and may be very much higher than the hospital costs. Some medicines subsidised by the government for other conditions can cost almost $19,000 per pack of tablets.