New study questions efficacy of antiviral Paxlovid in vaccinated adults

Despite a sharp increase in prescriptions for Pfizer’s antiviral COVID-19 drug Paxlovid (nirmatrelvir-ritonavir), a new study has not found a significant decline in hospitalisation or death rates among vaccinated older adults.

The study, led by Dr John Mafi, challenges previous findings that suggested significant benefits of Paxlovid in preventing severe COVID-19 outcomes.

“Since the strongest predictor of severe COVID-19 is advanced age, it has been crucial to obtain evidence on whether the results of the Pfizer trials generalised to older and vaccinated populations,” Dr Mafi said.

The findings suggest that while Paxlovid may offer some benefit, its impact on hospitalisation rates among vaccinated older adults is significantly weaker than initially reported.

“Our study effectively rules out the notion that Paxlovid causes large reductions in COVID-19 hospitalisation in vaccinated older adults,” Dr Mafi said. “While we cannot rule out a small reduction in COVID-19 hospitalisation, our results indicate that at best, Paxlovid’s potential effect on COVID-19 hospitalisation among vaccinated older adults is four times weaker than the effect originally reported in Pfizer’s 2022 clinical trial.”

In Australia, from 1 April 2023, the eligibility criteria for access to oral Paxlovid on the Pharmaceutical Benefits Scheme (PBS) was expanded to include people between 60-69 years of age with mild to moderate COVID-19 with one additional risk factor for developing severe disease.

Pfizer’s initial approval for Paxlovid was based on the Phase 2/3 EPIC-HR trial, which demonstrated an 88% relative risk reduction in hospitalisation or death when treatment was initiated within five days of symptom onset. The trial showed consistent efficacy across different patient profiles and comorbidities.

However, the latest findings raise questions about how these trial results translate to real-world evidence.

“Because access to Paxlovid in this study was in effect randomised for those close to the age 70 cutoff, our results are unlikely to reflect unobserved confounding,” said study co-author Sitaram Vangala. “This may explain why our results align with the recent negative 2024 clinical trial among vaccinated middle-aged adults, but not with observational studies showing that Paxlovid is associated with large reductions in hospitalisation and mortality in vaccinated older adults.”

Dr Katherine Kahn, the study’s senior author, stated “Since the study found no significant effect on COVID-19 hospitalisations and deaths among vaccinated older adults, our findings underscore the urgent need for further randomised-clinical trials investigating Paxlovid’s effects in higher-risk populations, such as older subgroups who are frail or immunosuppressed.”

In reimagining healthcare across the entire patient journey, Health Industry Hub^TM is the only one-stop-hub uniting the diversity of the Pharma, MedTech, Diagnostics & Biotech sectors to inspire meaningful change.

The Health Industry Hub^TM content is copyright protected. Access is available under individual user licenses. Please click here to subscribe and visit T&Cs here.