Abstract
BACKGROUND: Effective, safe, and accessible antivirals are needed to treat pregnant/postpartum (obstetric) patients with COVID-19, a group at high risk for severe disease. Newer antivirals (nirmatrelvir/ritonavir, remdesivir) are expensive and less accessible in low- and middle-income countries, including Brazil. Oseltamivir, a cheap, widely available, pregnancy-safe anti-influenza medication, was used off-label for COVID-19 in Brazil. The primary outcome was comparing in-hospital all-cause mortality in hospitalised obstetric patients with COVID-19 treated with oseltamivir versus no antivirals. Secondary outcomes were comparing the risk of progression to severe disease (ICU admission or death, whichever occurred first) and hospital discharge. METHODS: In this retrospective matched cohort study using Brazil’s national surveillance database (SIVEP-Gripe), we identified hospitalised obstetric patients with PCR-confirmed COVID-19 between February 2020 and October 2023. Patients first receiving oseltamivir on day zero of admission and admitted within seven days of symptom onset were matched 1:1 using propensity scores to patients receiving no antivirals at all. RESULTS: After matching, 445 oseltamivir recipients and 445 controls were included, of whom 79.5% and 80.0%, respectively, were admitted in 2020, and 65.8% and 67.9% had non-severe COVID-19 on admission (SpO2 > 94%). Oseltamivir use was associated with a lower risk of in-hospital death (hazard ratio [HR] 0.77; [95% CI 0.51–1.17], p = 0.22; absolute risk reduction [ARR] 3.9%) and progression to severe disease (HR 0.83 [95% CI [0.67–1.01], p = 0.07; ARR 4.5%) compared with no antivirals, though these associations were not statistically significant overall. Oseltamivir recipients were less likely to be discharged on days 0–2 (HR 0.68 [0.52–0.90]) but more likely to be discharged on or after day 3 (HR 1.30 [1.10–1.54]) than controls. Significant associations between oseltamivir use and lower in-hospital mortality were observed in two subgroups: patients admitted in 2020 (HR 0.54 [95% CI 0.32–0.93], p = 0.03) and patients with non-severe COVID-19 (SpO2 > 94%) on admission (HR 0.33 [95% CI 0.12–0.89], p = 0.03). CONCLUSIONS: In obstetric patients with COVID-19, oseltamivir used within seven days of symptom onset was associated with non-statistically significant lower risk of in-hospital death and progression to severe disease, compared with no antivirals. Results of this study do not support use of oseltamivir to treat COVID-19 in this population. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12879-025-12327-x.