Patterns of use of oral antivirals for COVID-19 in people 70 years and over in Victoria, Australia: a linked data study

Two oral antivirals for treatment of COVID-19 are available in Australia, nirmatrelvir-ritonavir, which is recommended, and molnupiravir, which is approved for use when nirmatrelvir-ritonavir is contraindicated. From 2022 to 2024, over 1.5 million Pharmaceutical Benefits Scheme (PBS) prescriptions were dispensed. We examined dispensing of antivirals in people aged 70 + years in Victoria, Australia, from July 2022 to April 2023. We linked COVID-19 notifications in residents of Victoria (population 6.6 million) aged 70 + years to data from the Australian 2021 Census of Population and Housing, Australian Immunisation Register, PBS and Medicare Benefits Scheme. We examined trends over time and compared the socio-demographic and clinical characteristics of people who received antivirals with those who received no treatment, according to the type of antiviral received. We also estimated the proportion of people that received molnupiravir and nirmatrelvir-ritonavir who had a pharmacological contraindication to nirmatrelvir-ritonavir. Among 76,120 people aged 70 + years with a COVID-19 notification, 50,005 (66%) received an antiviral with 37,101 (74%) receiving molnupiravir. The proportion of people that received nirmatrelvir-ritonavir increased during the study period from 19% (1957/10,256) in July 2022 to 35% (720/2075) in April 2023. After adjusting for age and sex, characteristics associated with receipt of antivirals included RACF residence, higher income and higher education. Compared to molnupiravir, receipt of nirmatrelvir-ritonavir was greater in those with higher incomes, higher education and no COVID-19 vaccine booster in the last 6 months. The majority of people who received molnupiravir (25,378/37101;68%) did not have a category 1 pharmacological contraindication to nirmatrelvir-ritonavir. During the study period, most COVID-19 cases in Victoria received antivirals but variations according to age, sex, socioeconomic status, residence in aged care and vaccination suggest that further efforts to identify barriers and enablers to treatment are warranted. Our findings also suggest that pharmacological contraindications to nirmatrelvir-ritonavir are not the primary reason for prescribing molnupiravir.