Evaluation of Nirmatrelvir-Ritonavir as Post-Exposure Prophylaxis for COVID-19
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Reviewed & Translated by Dat Tien Nguyen, B.A, ScM.
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Posted on September 2nd, 2024
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Given the emergence of new SARS-CoV-2 variants and declining vaccine uptake for the latest strains, COVID-19 continues to pose a public health risk. Since most SARS-CoV-2 transmissions occur before symptoms appear, individuals who have not received the most recent vaccines can unknowingly spread the virus. The nirmatrelvir-ritonavir combination has been shown to be an effective treatment for SARS-CoV-2. As a result, Pfizer sponsored a study to investigate whether this combination could be used for postexposure prophylaxis.
The clinical study involved 2,736 participants who had been exposed to a symptomatic, confirmed COVID-19 case within their household within the previous 96 hours. At enrollment, these individuals showed no symptoms and tested negative with a rapid antigen test. Participants were randomly assigned to receive either a placebo for 10 days or a combination of 300 mg of nirmatrelvir and 100 mg of ritonavir. Two dosing schedules of the antivirals were tested: 5 days versus 10 days. SARS-CoV-2 presence was monitored using RT-PCR and rapid antigen tests through day 14. With 3.9% of the placebo group testing positive for SARS-CoV-2, the study found that both the 5-day and 10-day nirmatrelvir-ritonavir regimens were ineffective as post-exposure prophylaxis, with 2.6% and 2.4% of participants testing positive, respectively. The authors emphasized that these findings are not definitive and recommended future studies with larger sample sizes to more accurately assess the efficacy of the antiviral combination as post-exposure prophylaxis.
The clinical study involved 2,736 participants who had been exposed to a symptomatic, confirmed COVID-19 case within their household within the previous 96 hours. At enrollment, these individuals showed no symptoms and tested negative with a rapid antigen test. Participants were randomly assigned to receive either a placebo for 10 days or a combination of 300 mg of nirmatrelvir and 100 mg of ritonavir. Two dosing schedules of the antivirals were tested: 5 days versus 10 days. SARS-CoV-2 presence was monitored using RT-PCR and rapid antigen tests through day 14. With 3.9% of the placebo group testing positive for SARS-CoV-2, the study found that both the 5-day and 10-day nirmatrelvir-ritonavir regimens were ineffective as post-exposure prophylaxis, with 2.6% and 2.4% of participants testing positive, respectively. The authors emphasized that these findings are not definitive and recommended future studies with larger sample sizes to more accurately assess the efficacy of the antiviral combination as post-exposure prophylaxis.