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Background: The safety, effectiveness and cost-effectiveness of molnupiravir, an oral antiviral medication for SARS-CoV-2, in patients in the community who are multiply-vaccinated and at increased risk of morbidity and mortality from COVID-19, has not been established. We aimed to determine whether molnupiravir added to usual care reduced hospital admissions/deaths among people at higher risk from COVID-19, and here report our preliminary analyses. Methods: Participants in this UK multicentre, open-label, adaptive, multi-arm, platform, randomised controlled trial were aged ≥50, or ≥18 years with comorbidities, and unwell ≤5 days with confirmed COVID-19 in the community, and were randomised to usual care or usual care plus molnupiravir (800mg twice daily for 5 days). The primary outcome measure was all-cause hospitalisation/death within 28 days, analysed using Bayesian models. The main secondary outcome measure was time to first self-reported recovery. A sub-set of participants in each group were assessed for the virology primary outcome measure of day seven SARS-CoV-2 viral load. Trial registration: ISRCTN30448031 Findings: Between December 8, 2021 and April 27, 2022, 25783 participants were randomised to molnupiravir plus usual care (n=12821) or usual care alone (n=12962). Mean (range) age of participants was 56·6 years (18 to 99), 58·6% were female, and 99% had at least one dose of a SARS-CoV-2 vaccine. The median duration of symptoms prior to randomisation was two days (IQR 1 – 3), the median number of days from symptom onset to starting to take the medication was three days (IQR 3 – 4), 87% (11109/11997) received their medication within five days of symptom onset, and 95·4% (n=11857) of participants randomised to molnupiravir reported taking molnupiravir for five days. Primary outcome measure data were available in 25000 (97%) participants and included in this analysis. 103/12516 (0·8%) hospitalisations/deaths occurred in the molnupiravir group versus 96/12484 (0·8%) in usual care alone with a posterior probability of superiority of 0·34 (adjusted odds ratio 1·061 (95% Bayesian credible interval [BCI]) 0·80 to 1·40). Estimates were similar for all subgroups. The observed median (IQR) time-to-first-recovery from randomisation was 9 (5–23) days in molnupiravir and 15 (7–not reached) days in usual care. There was an estimated benefit of 4·2 (95% BCI: 3·8 – 4·6) days in time-to-first-recovery (TTR) giving a posterior probability of superiority of >0·999 (estimated median TTR 10·3 [10·2 – 10·6] days vs 14·5 [14·2 – 14·9] days respectively; hazard ratio [95% BCI], 1·36 [1·3–1·4] days), which met the pre-specified superiority threshold. On day 7, SARS-CoV-2 virus was below detection levels in 7/34 (21%) of the molnupiravir group, versus 1/39 (3%) in the usual care group (p=0.039), and mean viral load was lower in the molnupiravir group compared with those receiving usual care [(SD) of log10(viral load) 3·82 (1·40) in the molnupiravir group and 4.93 (1·38) in the usual care group, (P Interpretation: In this preliminary analysis, we found that molnupiravir did not reduce already low hospitalisations/deaths among higher risk, vaccinated adults with COVID-19 in the community, but resulted in faster time to recovery, and reduced viral detection and load. Funding: This project is funded by the NIHR (NIHR135366). The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care.