If you’re aged over 70, or over 50 with underlying health conditions, and have tested positive for COVID, you might have been offered free or subsidised antivirals.

Earlier in the pandemic, these medicines were an important way to reduce the chance of people becoming severely ill with COVID, needing to be hospitalised, or dying.

But our new research suggests that with high levels of vaccination and immunity from previous infections, COVID antivirals are no longer working as well.

From no treatment to an effective one

When SARS-CoV-2, the virus that causes COVID, first emerged in late 2019, no treatment was available. Existing influenza antivirals, which had been stockpiled by governments, were ineffective and couldn’t be used.

Scientists rapidly tried to figure out which existing or new drugs could be used. In 2021, two industry-sponsored clinical trials reported promising results.

One was for nirmatrelvir-ritonavir (Paxlovid), which reported an 89% reduction in severe illness. The other was a trial of molnupiravir (Lagevrio), which reported a 30% reduction.

Paxlovid and Lagevrio work by stopping SARS-CoV-2 from replicating. So they need to be taken early in the course of illness – within five days – to be effective.

Both drugs became available in Australia and were listed on the Pharmaceutical Benefits Scheme (PBS) in early and mid-2022. This ensured people most at risk of severe illness had access to drugs at low or no cost.

Paxlovid and Lagevrio are expensive. A course of treatment cost the government around A$1,100 from 2022 to........

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